I've been renaming my boot hard drive since the System 7 days back in the early '90s. Same since installing the Mac OS X Public Beta in 2000. Ditto for pasting on custom icons.
It's perfectly safe.
…
For the most part.
The only
potentially risky thing is if you have spaces or "special" characters in the drive name. There was
the infamous iTunes 2.0 installer bug about twenty years ago where an Apple engineer failed to handle spaces in drive names correctly, and it could result in wiping your whole system. Whoops!
I haven't seen anything like that in a very long time, but I still stick to one-word drive names
just to be safe.