decking added then removed etc on vacating property

Tenancy Deposits

My tenants have just vacated my property yesterday. During the tenancy they (without seeking permission from us,) added some decking to the yard of the property. They also repainted the yard walls in a bright (garish) colour and added hanging basket brackets to the walls. The first we knew of it was when we received photographs from them of a 'before and after' by email, along with the comment 'any contributions are appreciated!'

We explained to the tenants that they should have sought our permission before making any changes/additions, as per the AST and that obviously we would not be paying for any work carried out in relation to this.

When checking the property after they vacated, we noticed that they have now removed the decking (!) and the hanging basket brackets (which have left holes in the walls.) Also, they have etched wording in an area of the yard wall (obviously when they had completed the work in the yard and as some sort of recognition of this (it looks like graffiti.)

Please advise if the tenants should pay for replacement of the decking, and also the repainting of the yard/any damage/graffiti which has been caused.)