Yes you can repack a bearing with grease if you're lucky.
BUT - Most of these bearings use races and bearings that are 'case hardened' only, that means they have a limited life and cheaper to make. So the repacked bearing may not last long anyway.
If you replace the bearing, don't use a hammer and a block of wood to slam it home, etc, bearings last longer if they are pressed in with an arbour press. You can grease up the bearing outside if needed to ease it in.
You can buy a cheap chinese arbour press and you'll find all kinds of uses that replaces a hammer.
I dragged out the one I made in high school machine shop, cleaned it up, put on a gun blue finish, added brass shim stock to tighten up the action and some grease in the rack, now it's smooth as can be !!!!