Actually, I kept on thinking "what might assist in this process you would want to achieve, something that goes against the Tanzimat?", and I realized - Mustafa IV. So, if I may propose a preliminary timeline:
* early 1797 - the military expedition of Hüseyin Küçük Pasha succeeds at conquering the Pashalik of Vidin, but fails to capture Osman Pazvantoğlu
** Prince of Wallachia Constantine Hangerli remains in power and doesn't get executed, as Küçük doesn't use him as a scapegoat for his failings OTL - make of that what you will
* summer of 1797 - Hadji Mustafa Pasha is appointed beyleybey of Rumelia Eyalet, and leaves the Sanjak of Smederevo for Plovdiv, to assist Küçük against Pazvantoğlu
* by early 1798 - the forces of Mustafa, Küçük, and the locals (Serbs, Bulgarians, etc.) defeat the fleeing Pazvantoğlu and his Janissary allies (including the OTL Dahije)
** for his efforts, Hadji Mustafa Pasha, alongside being the Smederevo Vizier, is maintained as beyleybey/vali for his exemplary work against the rebel forces
** Pazvantoğlu is likely executed, possibly the same for the Janissaries that helped him, getting liquidated
* Peace is restored in Rumelia Eyalet - the Serbs find rule under Hadji Mustafa rather acceptable, Hadji Mustafa remains a close collaborator with Selim III, continues centralization efforts
** elsewhere in Ottoman Balkans, eyes are locked on what's going on - Ali Pasha, the aristocrats of the Bosnia Eyalet, whoever is in the Silistra Eyalet, those in the Romanian principalities - Selim III is attempting to centralize authority, and reform the military
** meanwhile, the Napoleonic Wars happen as OTL
* 1806 - as per OTL, perhaps even emboldened by TTL developments, the Russo-Turkish War begins
* 1807 - the beginning of the Ottoman palace coups OTL
** Selim III is deposed by Janissaries led by Kabakçı Mustafa, replaced by his cousin, the newly named sultan Mustafa IV
** Kabakçı Mustafa is de facto ruler of Istanbul, Grand Vizier Keçiboynuzu İbrahim Hilmi Pasha is replaced with Çelebi Mustafa Pasha
** perhaps beyleybey Hadji Mustafa Pasha's rule indirectly led to Kabakçı Mustafa having greater forces TTL?
* Rusçuk derebey Alemdar Mustafa's counter revolt in 1808 is subverted - Alemdar, Çelebi and compatriots are killed, Selim III and OTL Mahmud II are murdered - Kabakçı and Mustafa remain unopposed in the capital
** Kabakçı Mustafa is named Grand Vizier, with deputy (sadaret) Köse Musa Pasha, the district governor in Istanbul
* Brief respite in the war with Russia due to the Treaty of Tilsit
* Status update on the Balkans:
** Silistra Eyalet and the Romanian Principalities: war frontier, occupied (directly/indirectly) - Scarlat Callimachi (Moldavia) supposedly stood alongside Selim
** Rumelia Eyalet: most likely under beyleybey Hadji Mustafa Pasha if he maintained his usefulness to Selim III, if not then someone akin to him; likely opposed to what happened in Istanbul
** Bosnia Eyalet: sigh of relief upon hearing what happened in Istanbul, İbrahim Hilmi Pasha is named the Bosnia vali by the Sultan in December 1807, with the banner of Herzegovina attached
** Pashalik of Yanina: Ali Pasha is very cautious, but intrigued by the happenings in Istanbul
** Morea Eyalet: I don't know...
* War continues with Russia later in 1808 - Mustafa IV and Kabakçı Mustafa try to figure out what to do with the Russians coming
* Mustafa IV sends out an ambassador to France to maintain their alliance (as per OTL)
* Ali Pasha tries to look towards the British (as per OTL)
Now, whether Hüseyin Küçük could've taken Vidin, I don't know, but this set of events seems convenient in permitting that Muslim Balkanisation you so wish. I'd suggest doing a lot more research, figuring out what parties are involved where (Hurshid Pasha and Ibrahim Bushat Pasha, as examples), checking many sources, identifying how titles functioned, were handed, and what the hierarchies are, if you really want to try and execute your ideas.