Unfortunately the Serbs followed a policy of "revenge for the Turks". Basicaly, since they cant reach Turks, they will put all their anger on Bosniaks.
Oh! Oh! Don't forget that they were brainwashed or educated (depends on your opinion) on the fact that Tito was a half-Croat half-Slovene, and that this was somehow bad.
As for OP's POD:
You're caught in a Catch-22 insofar as the liberality/appeal to the West of Serbia is concerned. If Serbia becomes a modern, more democratic state, then it's unlikely that it'll get involved in the war at all. If it gets involved in the war, that sets the West against them (say what you will about mujahideens and Muslims in Bosnia, the region and its capital of Sarajevo were well known for their cultural liberality).
As far as making Serbia more liberal/democratic, I'd say you should find a way to keep Ante Markovic's reforms in place. His stabilization of the currency and greater leaning toward the West greatly endeared him to the U.S. (well, and there were many who called him a CIA agent!), and prolongation and full implementation of these reforms could've outright avoided war with Bosnia.
Which is honestly I think the best scenario for Serbia at this time. Slovenia saw new markets and greater options in independence, and Croatia--with its tourism and fishing resources, and its refound nationalism--was veritably howling for independence; allowing those two states and Macedonia to succeed, and keeping Bosnia, would be a worthwhile and realistic goal.
Funny that the Serbia-saving reforms would be instituted by a Croat, but that's life, right? In addition to that, you can have Alija arrested/assassinated/whatever, and set Fikret Abdic to win the Bosnian presidency. He was all set in his little corner of Velika Kladusa with Agrokomerc, and was also a West- and business-oriented man. He was also very popular in Bosnia. In 1990 he and Alija Izetbegovic ran for the Bosnian Presidency of the Socialist Republic of Bosnia; both of them filled the two slots, and Fikret Abdic even won the popular vote to become President of the Presidency. For some reason though, he didn't win the "official" vote.
One theory is that the powers-that-were in the West wanted Bosnia to break away from Serbia; Muslim nationalist Alija Izetbegovic as President of the Presidency would have driven Bosnia to the brink of independence--and did. A group of weak, economically insolvent and dependent states in the Balkans were infinitely preferable to the West than another strong powerhouse-monster such as Yugoslavia.
Well, that's some info and a bit of help for your POD. Ante Markovic's reforms endure, and Fikret Abdic becomes President of Bosnia's Presidency.