1) Make it impossible for the Ottomans to annex the Crimean Khanate (which keeps them from constantly invading Russia) and eliminate the Eyalet mechanic for areas that were not Eyalets (Transylvania, Wallachia, Moldovia, and Crimea).
2) Let the Ottomans create vassals out of Algeria and Tunisia rather than annex them.
3) Reduce the ability of small countries, especially within the HRE, to drastically develop their small territories.
4) Make Austria more likely to win Imperial Elections, which they seldom do anymore.
5) Make it less likely for events like the "heir of another country" to fire, which has the effect of unhistorically altering the dynastic makeup of Europe, which was very static in comparison.
6) Around 1700, when Hanover forms, add an additional 8th Electorship for Hanover rather than taking it from one of the other 7 historic electors (make Austria more likely to usurp Bohemia's Electorate).
7) Make China more likely to form tributaries outside of China rather than conquer their territories.
8) Buff Persia to keep them alive between the Ottomans and the Mughals.
9) Make the Hussite provinces hard to convert as they were historically.