ive dismantled and done a few tanks now, nothing that small, mostly 55gals, and i will say, replacing the glass is not an easy job. bottom piece, probably the easiest, in terms of getting it apart, but it still a lot of work. having to break the silicone between the glass joins is time consuming and frankly, probably not worth the effort.
you could however use a new piece, plexi or glass, and yes, silicone it into the bottom of the tank.making sure to seal up around the edge good, so as not to allow water under it. you will need to cut and remove the existing silicone around the bottom edge though. not between the joins, just the bead, so the new sits flat.
that way, wont have to get the frame off too.
ive never done this method, but could see it working, in theory.