How Do I Edit The Map?

i want to add some little islands in the space of sea between sicily and cyrenacia.

a) how do i do this?
b) how much work is involved in doing this? e.g. adding the provinces and settlements, battle map information etc

thanks

i beg your pardon, i've found this link
https://forums.totalwar.org/vb/showthread.php?t=50437