
Not all dogs have rear dewclaws. Some breeds have it called for in the breed standard, so a lot depends on what breed you have. I have had a few pups born with rear dewclaws and I always remove them at 2 days of age, but always leave the front ones. My breed isn't meant to have rear ones and I feel they are safer without them, they do however use their front ones.
I had a rescued Border Collie once who had rear dewclaws, and I simply asked the vet to remove them at the same time as she was spayed. If I was you and your breed is one NOT meant to have them, it's probably easiest to ask for them to be removed when you have something else done rather then make it a separate thing. It's a quick job so shouldn't be a problem for the vet.