Flooring

Tenancy Types and Management

My tenants have just moved in beg of Feb. The whole house has laminate flooring apart from the stairs. They have text me this evening to ask if they can put down some carpet in the bedrooms as the floor is noisy and creaky and ask if i will pay half. I have said no and also that i dont think i want carpet. She has now said she hates laminate and did not think i would object and they have to live there. She has also said that they would put the laminate back when they leave.
My worry is that if i say yes and they take it up in both bedrooms if they dont store it properly and it warps and is not right when they relay it etc. Can i draw up an amendment to the contract that they sign to cover myself and what wording is legal.
To be honest they have only just moved in and the contract is for 6 months i have served a section 21b notice so we can have a rolling on contract after as they wanted to stay for 5 years. they viewed the property 3 times before they made their minds up and not once whilst viewing did they mention the flooring. I would be inclined to make them stay the six months first and then see whats what. Any advice would be appreciated.