Can things on the contract change? Let’s say I put a property under contract, and I go to assign it, but my partner would like to make changes to the contract. Would that be possible?

Yes, things on a contract can change, but only if all parties who have already signed the contract agree to the change. This can be done by making the edit on the contract and then having all parties initial by the edit which signifies they approve. Or, you can have an addendum created. An addendum is a separate document outlining the changes made to the contract. Once again, this addendum has to be signed by all parties to be valid. No changes can be made to the contract unless agreed upon by all parties!