Keeping a mortgage to avoid fees of a new mortgage certificate?

My parents have a very small mortgage (50k CHF). Now that their (marginal) tax rate has plummeted with retirement, they would like to kill off the mortgage entirely to save around 1.5k CHF in interests. In a few years I would like to purchase their house and I will need a mortgage.

Would it make sense to keep a very small residual amount on this mortgage (e.g., 1k CHF) to avoid killing the mortgage certificate / Grundpfandrecht / cédule hypothécaire?

I found online that it would cost around 2% of the mortgage amount to create a new one, but I don’t know what it would cost to reuse one and changing names, banks, etc.

Thanks for your help!

The Schuldbrief doesn‘t get „killed“ by paying back the whole amount. As soon as the bank doesn‘t need it anymore (no mortgage), they will send it back to the owner of the property (your parents).

Later you can just go to any bank with it to get a mortgage.