Well,pretty much explained in thread title. Why? Well,in racing heat it happens that finger slips when you change between damage repair option and suddenly you end up changing the assymetric tyre setup to symetric. Changing back it does not change to previous assymetric setup,so you're stuck with screwed up setup (unless you remember setting of every tyre) and mandatory setup change with damage repair you don't even need... (like I did today and quite few times before) Of course some might have made changes too much and would be much easier to reset those changes with single option change,as it's still quite easy to make mistakes during racing.
Should be an "easy" addition,I suppose...

I would agree but what do you mean by "request to F12 menu"?

In F12 you can see all the setup settings which are valid when you leave the pit.
If you change for example tyre pressure to some other value it is a request to be done when you next time go for a pit stop.

What I would also like to see on top of Rony's suggestion is the request made for example changing the tyre compound would not trigger damage repairing.
Sometimes there is races where you are forced to change the tyre compound into another (rule for that race) and if you have any damage those will be repaired aswell although they would not influence much on race performance.

Oh, so it's not about a setup menu (shift+p) at all, my bad.
In that case I would also suggest to add an option to cancel setup changes in setup menu.

Quote from LakynVonLegendaus :

I would also suggest to add an option to cancel setup changes in setup menu.

This one is already there if you mean in pits (shift+P) - when you change something,a button "cancel" is shown next to "new setup". (it's not there when you haven't changed anything yet)

Quote from Eclipsed :

This one is already there if you mean in pits (shift+P) - when you change something,a button "cancel" is shown next to "new setup". (it's not there when you haven't changed anything yet)

Wow, I'm so noob. Yes there is an "Undo" button. Never noticed Thanks for the info then