I have done this often, although always with Partner Gold or above status on my DL Skymiles account.
I find the best way is to leave the VA number on the reservation until you are in the lounge (assuming it is a VA lounge). Then after entering the lounge, ask someone at the service desk to put your DL number on the reservation, instead of VA. I've probably done this a dozen times, sometimes it is quick and easy, sometimes the staff are unsure what to do, but they sort it out. Always ask for a new BP showing your DL number to be sure it was done properly.
My DL status always allows VA lounge access anyway, so you may get some question if yours doesn't, but IMO you still are allowed access and of course once you are in the lounge it should be easier to stay there.
In terms of boarding, just have your VA card ready along with your BP just in case.
I've only had one 'bad' experience, where at SYD the gentleman said I wasn't allowed to keep my EconomyX seat if I took my VA number off the res. He was a little rude about it, like I was trying to steal the seat. I politely said I was still a VA plat, regardless of if it was on the BP or not, and I have never seen a requirement to credit to VA attached to this benefit. He said sorry, it isn't allowed, he has to re-seat me. So I said nevermind, if he wants to treat a Plat that way just leave my VA number on the BP, I'll keep my seat. Then he said the classic 'as a one-time courtesy I'll let you keep your seat'. Thanks mate.