Under Renting Homes (Wales) Act 2016, once a contract has been agreed upon, it can be varied but only where the legislation allows. There are provisions for altering the rent and other terms. Some terms can never be changed even if both parties want to (except if varied by legislation).
Government websites are creaking under the strain as tens of thousands of well-wishers rush with open arms to welcome refugees from the war in Ukraine under the Homes for Ukraine scheme.