I don't know about 90% but you can certainly have a more Monarchical Africa. Avoiding the circumstances that led up to the removal of the Monarchies of Rwanda, Burundi, and Uganda would be good but they might still suffer the same problems their Republican variants have IOTL. Same thing with the Solomonic Dynasty and others.
Ethiopia - At the very least, avoid having the Derg remove the Monarchy. That can happen by having
Amha Selassie accept the Derg's offer to succeed his father and push through necessary reforms like those the Derg did, albeit less radical. I'd recommend a POD prior to 1900/1935 to avoid the situation the Solomonids were in by 1974-75.
Rwanda - If
Rudahigwa can push through substantial land reform to make up for his decree's shortcomings and get the support from his Hutu subjects, I see the Rwandan Monarchy remaining in power with the possibility of the 1959 Revolution (more of an uprising, really) being sidelined. His successor, Kigeli V, was also initially popular with Tutsi elites, Hutu nationalists, and the Catholic Church so he'll probably be a good candidate to unify Rwanda under the Monarchy instead of seeing it torn apart. Having the Rwandese National Union clamp down on the worst of its rhetoric would help it to power and act as an arm of the Mwami in uniting Rwandans.
Burundi - No Belgian assassination of Crown Prince Louis Rwagasore in 1961 would help to facilitate a stable Burundi that avoids its pogroms against its Hutus. His Union for National Progress was certainly popular enough to continue winning after his death so combined with a surviving Rwagasore, I can see the Burundian Monarchy remaining in place instead of being removed entirely in the 1960s.
Uganda - I'm actually not completely sure about this one. A wider Kabaka Crisis or Mengo Crisis might see Kabaka Mutesa II and/or Grace Ibingira prevail over Milton Obote as the Kabaka Yekka Party somehow gains a victory over the Ugandan People's Congress. You might avoid the worse of the Ugandan Bush War or see it become more violent.
Ghana - Have the restored autonomous Kingdom of Ashanti play a larger role in the politics of Ghanian independence. Prempeh II seems like a good candidate.
Something could also be done with Dahomey, Kongo Kingdom, etc. but that might require a pre-1900 POD.