I do not recommend it! A lender can pull their credit prior to (or the day of) closing if the original information on the Mortgage approval changes. Making big financial commitments like a car or financing furniture result in the file going sideways.
If you find yourself in a similar situation, speak to your Mortgage professional before making such a decision.

Yes, your income dictates the size of Mortgage, hence a Mortgage helper adds income to your application and increases your Mortgage qualifying amount as long as it’s a self contained unit with a separate entrance, kitchen and bathroom.