I'd like to change the Scottish League setup - from 12/10/10/10 to that of another country, like Denmark 18/20 division setup.

How would I go about this?
How do regens work?
Does this sort of thing affect the national team?

Can I clear domestic competition histories, increase UEFA coefficient, decrease time for passport/2nd nationailty, alter TV income etc easy enough with the editor, or do I need patches?

Appreciate any guidance, not really modded the game much before.