Well it would delay the closing. All the paperwork and everything has to be re-done. Also if the amount is less than originally approved for then it could mean the loan process has to start over.

How much difference are you talking about, and when is the closing?

If you want to increase the amount that you are putting down, it will require redoing the paperwork. If you want to increase the amount of financing, it will put sand in the gears, cause a major delay, piss off the seller, piss off the mortgage lender and piss off anyone else waiting on a check from the transaction.

It would be 5k less

OP is saying they want to put $5k less down payment on the purchase which means $5k more mortgage. This means going through underwriting again which would cause a delay. What happened to the $5k that you showed the lender you had available to close? That will be the very first question asked by everyone - especially the lender. Agree with homechef59, this would not only cause a delay (and cost more money for doc prep and other fees) but piss off everyone involved in the transaction.

One more comment: As of Oct 2015 and thereafter your lender is required to send you the CD (Closing Disclosure) prior to closing. You have to have it in your hands at least 3 days prior to closing. So if the CD is changing you will have to go through that process again in addition to the underwriting. Here is a good explanation about the 3 day requirement: https://www.consumerfinance.gov/ask-cfpb/what-should-i-do-if-i-do-not-get-a-closing-disclosure-three-days-before-my-mortgage-closing-en-1911/#:~:text=Your%20lender%20is%20required%20to,are%20what%20you%20are%20expecting.