Flexible rotation size, strict 4/5
 

I play mostly pre 1950. I use strict 4 man rotation which generally works out fine. Sometimes though after playing 10 days or more in a roll, all my starters will start the game with some degree of tiredness. It would be nice if the AI would switch to a 5 man rotation until there is an off day and then switch back to the 4 man rotation.
Maybe name your 4 starters along with a spot starter. The spot starter would not be used for an injured player but used to give all the listed starters an extra day off.
Basically, if a team has 4 games without an off day, they would stick with the 4 man rotation. If they go 5 games or more without an off day, then the spot starter would start the 5th, 10th game etc. until the next day and then the next pitcher due up in the rotation would start the game following the off day.

Why don't you switch to a 5 man rotation?

I want this to be league wide not just for my team. I play mostly between 1901 and 1960 so a lot of the 5th starters are pretty crappy and want to use them only to insure the others get 4 days off.

Setting a reliever to "Emergency SP" basically means they are your spot starter if it comes to an SP's turn and they are fatigued IIRC.

But that wouldn't go league-wide unfortunately.