Well, those event ids are within the reserved Paradox space. There are already events that have those id numbers. Add a zero to the end, and you should be fine.
In general, I'm not sure about all the consequences of your event choices. For instance, keeping Demetrios would probably increase stability (no changing of monarchs), but if anything would decrease centralization (that slacker isn't going to be able to keep hold of power).
Aristocracy is a good slider to play with, since the nobles will have a preferred candidate who you either accept or ignore. Stability, likewise, with any change causing a hit.
Instead of centralization, I would suggest maybe quality or serfdom. An inept, autocratic leader would mean -1 quality, +1 serfdom, perhaps. I would also generally limit DP slider movements to 1 or 2 (for major changes), since you are only choosing a monarch, not reorganizing society.
Also, the Byzantines might not have Thrace (prov. 357) anymore in 1453. They probably won't. It might make more sense to just remove province triggers, so change the province concerned to 360 (Morea).
I hope these criticisms don't sound negative - they're not! These look like good events. Do you know if your new monarchs conflict with the monarch list of David Comnenus?
driftwood