Hello,
I did a few quick searches of the forum and found this thread where a similar suggestion was made -
https://igpmanager.com/forum-thread/54272
A repeated argument against having the ability to set individual push levels for each stint is that this game is designed to be played online.
Implementing Push Level options for each stint in auto setup takes away one of the advantages that attending races live gives you.
If people are unable to attend races live, they should have to pay a small 'price' for not being able to sacrifice some of their time to race live. Managers who find themselves failing to attend a lot of races may need to look for a league that races at a more suitable time.