Go to your Europa Universalis/Scenarios folder and make copies of the "Grand Campaign.eug" and and the "1492.inc".
Rename your copies to "Byzans.eug" and "Byzans.inc" respectively.
Both files can be opened and edited with notepad, which is what we will do.
In Byzans.eug, change
name= "The Age of Exploration" to
name = "Byzantium", change all instances of the tag TUR to UKR (or at least the
TUR = { into
UKR = {) and finally change
include = "scenarios\1492.inc" into
include = "scenarios\Byzans.inc".
Then go to your Europa Universalis/config folder and make a backup of your "text.csv". Open your original "text.csv" and search and replace
UKR;Ukraina;X;X;X;X;X;X;X;X;X;X with
UKR;Byzantium;X;X;X;X;X;X;X;X;X;X
If you want the flag and shield to be correct anyway you can download the Byzantium shield set from Jeremy McGuinns page, here ->
http://hem.bredband.net/b103277/graphics/jwm2.html (very small .zip file)
Rename his flags and shields, changing the tag BYZ to UKR.
Then the flag_UKR.bmp goes to the Europa Universalis/GFX/Map/Flags directory and the other three go to the Europa Universalis/GFX/Map/Shields - rename the original files by adding the word "backup" to their names first.
Now there is only one question remaining, how to edit your "Byzans.inc", and to know that we need to decide how large Byzans should be, should it be only the city/one province or should it replace the Ottomans completely? And which particular provinces should have religion changed? etc.