New credit after mortgage offer

Hello. I have just received my mortgage offer from Halifax but i would like to extend my overdraft before completion.
I do have all my funds to complete so this has nothing to do with the purchase.

Would this be a bad idea to apply for more credit?

I understand that they can do multiple credit checks before completion and i just wanted to confirm if this would be too much of a risk as i wouldnt want them to amend or withdraw their offer.