Is it haram to cheat and if so what is the punishment?
If there was a condition in the Muttah contract that the male cannot take another partner and he breaks the contract and does, what’s the ruling/punishment?
As well if he forced the girl to change her mahr and kept prolonging giving her it?

All of the above is haram and in regard to the last question the whole contract becomes questionable and the mahr must be paid otherwise the relationship is bordering a haram relationship