Add Teams to League on Editor

Hello

Does anyone know how to add more teams to a league on editor, for example the welsh league only has 12 teams but I want to increase that to 19,

Any help would be great

Thanks in advance

I re-created all scottish leagues in the last version of fm. If i remember right you use the nation rules or there is some way to build your on league which will over right. i am sorry that i cannot remember fully but it is possible.