Creating maximum foreign (non-EU) players at club rule to existing league

[Zek]

I would like to add a rule that every club of a league is allowed a maximum of three non-EU players in the squad, like what Spain has, but I was wondering if I can add the rule to an already existing league? And if that's possible, how? Or do I have to rebuild the league from scratch if I want to add that rule?

Thanks in advance.

[Roy Race 9]

via advanced rules no need to rebuild comp will take seconds to do 

edit fixture rules for the comp concerned as below

this has been asked many times use search function to find the answer mate