I wouldn't worry too much about it as long as you do the adding before the roses break dormancy or, if you leave it until autumn, after they become dormant. Presuming you planted them with the bud union 2" below grade in the first place, which is what you need to have done for them to weather the winter and still live, another 3 or 4" shouldn't do them much harm, though you might want to do it in stages over a couple of years. The benefit to all of this, of course, is that the roses will eventually be growing on their own roots if they aren't already. What you might want to do (and I often do with potted roses I want to plant deeply but waited too long to plant in the spring) is add 2" soil around the canes and the surrounding area higher, filling the remaining holes in the fall after the little darlings have gone asleep for next winter.
Steve.

I hope you'll forgive my want of courtesy -- you're welcome.

Thanks for the response, and ... ok?

I particularly like the idea of filling around them then bringing that level up over a couple years. When they were given to me I knew nothing about plants really, I'm still overwhelmed by all the info on the forums here, but I didn't know about a bud union or any of that. I do believe they are a few inches below surface though, as my wife suggested I not plant them as deeply as I had planned.

Since Thanksgiving I've had a few inches of mulched leaves around each one to protect against temperature changes during winter. Maybe I can get away with adding some soil around them right after removing the leaves, and it'll be close to having added the soil during dormancy, but taking a couple seasons does seem safer.