Travel Management - Cancel Trips and FI documents

Hello,

I would like to know if once Travel Management trips have been posted completely in FI (the cycles have run) they can still be modified?

If yes, how: if we cancel the already posted trip in Travel Management, does it cancel FI documents? Until what point in the workflow can we modify the trip data?

Moreover, I would like to know what messages are parameterized by default in TM, and how we can modify them?

Thank you very much.

Jerome