Transplanting Perrenials - Lavenders

Someone, anyone, help! I really need to move 2 spanish lavender plants that are near the front of my flower border and too large for the space allotted and replace them with munstead lavenders. I want to do this today while I'm in the yard. It's so beautiful out. Is it too late in the season to do this? We are having frost tonight, but I can cover them to protect them. This is my first year with lavenders and I'd hate to lose any of them. Or would it be better to just place the potted ones in the ground and wait until spring to transplant all of them. Any suggestions would be appreciated.