Yes, this is fine. Users with access to moderator tools (10k on full-blown sites, 2k on beta sites like Earth Science) even have a special tool for this:
Inline tag editing
Finally, you now have the ability to do inline tag edits on questions: a new "Edit tags" link will appear next to the tags on every question; clicking it brings up an inline editor for the tags on that question:
This allows you to quickly retag questions that need it, which you'll find especially useful combined with the list of new tags on the stats page.
Such a tool wouldn't make sense if it wouldn't be correct to leave the body (and the title) alone.
Of course, as with all edits, it's best to
- try to improve as much as you can, especially when you don't have full edit privileges yet
- not to edit too many questions at once, to avoid flooding the review queues and/or the homepage with old bumped questions