I think the rule is you would need to get the financing company to provide a letter stating how much the monthly payment would be if you didn’t have deferred payments. That amount is factored into your DTI. For income based it might be similar if you have a 0 payment. I’m not sure about switching it to 5.
They won’t accept 0 as your “monthly payment”. They want to know what it would be if it were not deferred. They factor in a phantom debt so worst case scenario you have to start paying off your loan with your current income you could still afford to pay your mortgage with no issues.
You do not have to actually start paying off your loan.
A zero student loan payment is not acceptable for calculating your affordability in the NACA program. There are in fact several ways of determining a non-zero payment figure and yoru counselor can help you determine the appropriate one to use.