Creating / Adjusting Nation Rules

I'm revamping the Australian league by giving it a second division a little bit more money and more reputation. I soon realised I needed to adjust the nation rules. It says that the date range 01.08.11 - 30.05.12 isn't big enough to be able to schedule 90 matches**? Could I get some assistance with this?

you probably need to make a new league for that.