It would be good to have an option to have 5 subs come on if this were possible. It would help me, but i would need to get a few more players to make the most of this. 
The positives are you could rotate your squad more to have your players available more. But the negatives are that those powerhouses with a good squad of 20 available players would be strong virtually all the time making them harded to get results from. 

Being in Div 3 that will not be an issue for myself. But it could lead to the same teams being powerful for longer than normal. 

Maybe have an option for 5 subs in Division 3, 4 in Division 2 and the minimum of 3 in Division. Cup games all at 3 subs only. The lower league teams could then be more competitive in the Cups as they could rotate and have more of a go in the Cups. 

Not sure if that is possible to even change the code.