Impossible to change method of acquisition when under contract?

[Omer H.]

Hello BP! 

My business partner is currently under contract on a property using a loan from a portfolio lender. However, an opportunity has come up where the seller may agree to let my partner "assume" her existing mortgage on the home. 

My question is, is it impossible to change the method of acquisition when already under contract? If not, how does that process look like?

I was hoping to learn more about this or if this is even possible before the seller potentially agrees.

Thank you!