I say do it if you want. It's your gun and I agree with your logic. It's minimal effect on the gun (done correctly) and advantageous to you.
I work with guys who use their 416's daily. The PMags they do have (if not EMags) are modified from the command. Their support guys use standard M4's/un-modded PMags. What happens when they get in a TIC and have to use "other/un-modded" mags?
If I owned an MR556, I'd go this route.