We could see something along the lines of Islam becoming a "Fourth Teaching" to complement Buddhism, Taoism, and Confucianism. Islam would be thoroughly Sinicized, with "Hui" becoming a major branch of Islam. They'd probably drop more Arabic and Persian as the Hui are more integrated into Chinese culture, retaining only a few key religious terms such as Allah. I'm sure it would be scandalous at first as the Emperor dons a white cap and builds madrassahs and mosques everywhere, but the Yuan were fairly religiously open(leaving the status quo religious freedom) and as long as the Hongwu Emperor does his Emperor's duties and pays heed to the most important Confucianist mandates then he'll be fine. I could see it becoming somewhat of a family tradition to learn about or patronize Islam, but not all Ming Emperors will be practicing Muslims past the Jianwen and Yongle Emperors.
The most important change will probably be expanded contact with the West. If Muslim merchants gain special privileges and send word the Emperor of China is a Muslim and China is now a Muslim land, it will definitely impact people like Timur and Murad or Bayezid Osmanglu. Timur might try to conquer his way to China to meet his "Brother in the Faith" and establish overland trade relations that collapsed during the Red Turban rebellion. I doubt he would repeatedly murder the envoys of a fellow Muslim. Either way, the attempted conquest of Ming China is most likely butterflied and thus, the method of his death. Timur's life is as long as the writer wants it. If he does decide to ally against instead of with his fellow Mongols then this would probably take his attention away from his later conquests in either Anatolia or Delhi.
Chinese history doesn't change much for the next 100 years besides some court drama, an extra rebellion or two put down by the same elite Muslim Hui and Uygher troops and then some neat new architecture and poetry. Timur's relationship to China changing changes an absurd amount. If Timur focuses on the East and splitting Central Asia with the Ming, then Bayezid Osmanglu will probably take Constantinople 50 years early. Establishing himself as Roman Emperor and Caliph shortly after defeating a Crusade in Nicomedia would be the ultimate affront to Timur's sensitive ego, who could barely stand another man claiming to be Emperor of China, let alone his rival Bayezid capturing the Queen of Cities and claiming authority over him. He would drop everything and attack full-force at the Ottoman Empire. Bayezid's huge support among the Ghazis would come into play here. He gathered an army of 85,000 against Timur OTL. As Emperor of Rome and Caliph he would most definitely be able to muster thousands more Ghazis from all over and could afford thousands more Janissaries and Saqaliba thanks to the generous donations of the Greeks. And since Bayezid is even more powerful than OTL, I would bet Timur wouldn't be able to recruit as many of the Turkic Beys to his side. This would lead to roughly equal forces, the greatest armies of the world, led by two great conquerors.
The battle will go whichever way the writer wills it. Timur outsmarted Bayezid OTL, who was arrogant and did not listen to his generals when they said to stay on the defensive and lure Timur to a more advantageous position. Bayezid took his tired and thirsty army and charged it right into Timur, who with greater numbers and mobility, slaughtered his army. Though this time it can go either way. Bayezid could be not so hot-headed, as he was forced to abandon his siege of Constantinople to deal with Timur's invasion OTL, but now is the Roman Emperor routing a barbarian invasion(ignore that they're both Turks.) Also it's past 1400, horse archer armies aren't invincible like in 1260. Lure them into a confined battlefield, like they did historically, and a few good heavy cavalry charges can chase them into waiting infantry and foot archers. That was the original plan, use the high ground and greater range of foot archer Janissaries to keep Timur from hit-and-runs, then force a melee, where the heavy infantry and cavalry can slaughter them like the legendary battle of Ain Jalut where the Mamluks defeated the Ilkhanate. So I'll let the Ottomans have this one. They capture Timur and he dies shortly of pneumonia he caught from being in the Tarsus Mountains at such a ripe age.
Bayezid the Great hears from Timur and his men that the Emperor of China is Muslim and sends an expedition(with gifts) over the sea from Basra(Central Asia is now in chaos) to inform the Huángdì that he was Caliph and thus, like totally his boss kind of, but as Roman Emperor he was his equal. The Yongle Emperor, who is now and forever shall be the most Muslim Huángdì that ever lived(thanks to the support of the Eunuchs, who took to Islam like a fish to water) is delighted to see an actual expedition from Daqin, not heard from in centuries, and even better, their Emperor is a Muslim. He ends up greatly offended that the Caliph could claim any authority over him, the Son of Heaven(metaphorically, of course) and sends demands to Bayezid that he cease claiming authority over him. In an astounding act of humility and graciousness, Bayezid sends an apology, and more gifts, asking for silk and porcelain in return.
Bayezid dies of liver cancer before his merchants can make it back, leaving the throne to Isa, who has killed two of his brothers already, convincing the other brothers not to try anything. Isa finishes the conquest of Wallachia and tidies up some of the remaining beys and Greeks before he dies in a freak sauna accident at only 39, leaving his young son Mehmet on the throne and forcing a civil war between his remaining brothers. Little Mehmet actually wins, thanks to the kind support of the Janissaries who in their gracious magnanimity took on custody of the poor boy and guarded his August Personage and Constantinople from treachery. The Turkish Empire soon becomes a state that would not be unfamiliar to the Japanese, with the Emperor pampered and confined to the Topkapi Palace while the Grand Vizier(the Emperor always picked a Janissary for some reason) truly ran things.
Back in China, people got used to a Hui Emperor pretty quick(still better than the damn Mongols.) Mosques are in many cities, thanks to converting becoming socially acceptable. Yunnan is very Muslim, thanks to the original colonists being Hui and most of the Han colonists converting upon arrival. But Hui Islam became increasingly divergent from Arab Islam. There became less and less scholarship on the Quran and less focus on the Shahada and more and more focus on the Hadith and Sunnah. As Hui Islam integrated even more with Chinese culture, it adopted more and more the characteristics of Chinese philosophy. Especially a focus on filial piety and cultivating virtues. As the Buddhists attempt to escape karma by emulating the Buddha, the Daoists to achieve harmony with the Dao through wuwei, and the Confucians to achieve society harmony though cultivation of virtue and maintenance of ethics, Hui Islam attempted to earn a place in Jannah(heaven) through cultivation of virtuous traits Muhammad exhibited or advocated for. Although this sounds just like Sunni Islam, all Ijma, or consensus within the faith, comes from the Chinese Ulema(religious community,) not from the Sahaba or Salaf, the original few generations of Muslims. The Hui Muslims even ended up with some Hadith that cannot be found anywhere else in the world. This meant the behavior deemed good could be pretty far divergent from mainstream Islam.
I'd go on but if I wrote any more I'd have to start my own timeline.