Alternate Christianization of Balkans

Hello, I want to write a TL focused in a alternate south slavic nation replacing Bulgaria on a early conversion move.

Now, I need some fresh ideas on how could such ATL bulgaria-a-like develop its culture and religion having another ground for the byzantine eastern rival-and-friendly neighbour pack.

My will is to make some ASBish early unification of the illyria-dalmacia-pannonia provinces (a proto-medieval Croatia) by an slavonian perun-send knyaz and some goes-bad affair after sucession that forces christianship in a basis of political need/divine signal to victory in battlefield.

I know about the giant hurricane of angry butterflies from displacing the heart of slavic christian world past-in-time (800/801 conversion? IDK) and west-in-map (Zadar? Spalatum? Zagreb?).

Some good points to clarify:

1) How alphabet will develop? This changes everything about how glagolithic and cyrilic developed OTL. What alternate elements the one eye on west and another on east could bring? How is the state of the early settler peoples in Balkans? Will avar influence replace bolghar one in this scenario? Gepids, lombards and ostrogoths still present at this point in OTL?

2) How native society might look apears? Instead of the frank-way we get an byz outlook on a slavic chassis? This could some way ending as the east-slavic descentralizated proto-state or more like Bulgaria itself? An Slavonian Empire replacing Bulgarian-one with it own domestic patriarchate and aquiescense of Constantinople? Bulgaria itself will hurry up to embrace christianship? To remain pagan due to the two-front issue? To assimilate on the slavic majority? Or to remain distinct due to the "slavonian claim over christian slavs"?

I'm drowning in this topic and the timeline is already beeing write, but I want to trash it with maps and ilustrations together. I need more research and confidence before start it again and urges all of you not-so-early medievalist to help.

(sorry anything, I'm new here and my english is from the latine third world poverty against the need to learn history)
 
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