Hi @Kat15786
I don't usually host long stays, so others may be in a better position to advise on that aspect.
But for a booking of any length, keep two things in mind when someone wants to shorten a stay:
the potential impact on the review, and the fact that they may actually stay if you don't let them shorten it (in other words, do you want an angry guest to stay the full 5 months).
If you agree to a shorter stay, go to the booking, scroll down to Change Reservation, Change end date and you can modify the amount on your end. The system will then send the changes to the guest for approval.