It could affect you process? They very well may run and update your credit just prior to final loan approval, especially if there are some unforseen delays in the process that makes your current credit report out dated. My suggesstion and always the rule of thumb in todays times especially is DO NOT DO ANYTHING DIFFERENT DURING THE PROCESS, do not buy car, make application for credit card , or any other types of loans. After closing is another story, you can do what ever you wish. Mortgage lending has changed so much the last couple of years and they are going over people with a fine tooth comb and double checking the whole process. So my advise is to Not do any cosigning until after the process is over. If I can help with anything at all let me know.