I don't think anyone would love you for it, but since PM&R is usually an advanced program (you are doing an internship first anyway) you likely could get out of it later.
I would keep something in mind, however. This situation reminds me a lot of colleagues who talked it up for the admissions committee and then tried to transfer to an allo school because they didn't want to be DOs. Basically, those students stole a spot from someone who really wanted to be a D.O.
If you take a spot in PM&R (and you'll have to talk up your interest and motivation and experience for it) and then drop out, you really have taken a spot from someone who wanted to do rehab.
Only you can make the decision.