How will the added payment affect your DTI ratio? This plays an important part of being qualified for a home.
If it were me and there was any possible way that you could wait until after you got the mortgage, I would.
When I spoke to a LO at BoA last summer, just getting some estimates and feel for things, she said they wanted to see that I hadn't take on any new debt in the last 90 days(I think). However, this could have been because if my DTI, my credit, etc. Any number of reasons.
I wouldn't risk it, but you have to do what you have to do.
Possibly move the mortgage and do that sooner?