The pit confirmation voiceover is turned off in P&G yes, but if the pit light is on your crew is ready, requesting pit stop while the light is on will cancel the request as you described.

In the XD-Tool you can cycle to the 2nd page for pit options with a dedicated key (usually the one below Esc, whatever that is depending on your keyboard layout ). As that key is dangerously close to accidentally pressing Esc I'd open the XD.ini in your GTR 2 install folder and look for the keybind and change it to some other free key by putting in the number for that key instead.
I for example have a US keyboard layout so I bound it to above the Enter key, far away from Esc.

On that 2nd page you navigate with the arrow keys down/up and left/right to decrease/increase/turn off things