Personally, I'd have the PoD be that instead of trying to take Egypt and the Holy Land - have Manuel Komnenos fix at least two things
1) Michael Palialogos needs to be reminded to be less abrasive - if he can avoid alienating his allies in S.Italy, then that will certainly help there - and keep some Byzantine forces commited in Italy and Sicily long term.
2) Directly attack the Dashmenids (or however it is spelt) - this circumvents the initial issues with the Sultanate of Rum, who for the sake of this, are still defeated in the first round, and nominally submit. Manuel takes the Dashmenids, on, wins, and stablises Anatolia.
3) There is now a ticking time bomb. Any Emperor stupid enough to try and force the Anatolian Turks to convert is risking everything, inevitably, one will appear - perhaps an arrogant zealot, or any number of reasons.
Pisses off the largely Greek-Speaking Turks. They are still Turks, rather than Greeks, but a lifetime working with, and speaking with Greeks in Greek makes Greek a more important language for them to learn - but after a rebellion, most of their records, and retained knowledge is in Greek - perhaps there is even a Greek 'Turk' leading the new state, but a Muslim.
So a Muslim Greek-Speaking Turkish State emerges in rebellion, shattering an Empire.
NOTE : 1) is important, as it distracts resources from elsewhere that would make the rebellion easier to stop. I'd assume a rebellion would work best when the Byzantines get themselves embroiled in an Italian War.