Tenant wants to put wallpaper

My tenant has recently made a request to allow her to put up wallpaper in lounge room on one wall.

This is a long-term tenant who pays on time and have had no issues with and would like her to stay, in principle I have no objection to it other than the fact wallpaper could be messy when removing.

Is it wise to take a small deposit upfront to cover the removal? would this be have to be protected under a scheme or can it be a written agreement between us?