wrong commit/ seeking branching advice

[cc]

Hi,

I made a mistake in committing a change to the main trunk,
when I should have committed to a branch.  I created the
branch, but forgot to retrieve the branch's version.

Is there a way to reverse the changes, or at least move the
changed revision from the main trunk to the branch?

Also, with regards to branches, I'm a little confused with
the manual's rationale for doing branches.  I'm doing
a database application which uses local tables via local
table drivers (specifically, BDE) but I'm migrating
it to use MySQL on a central server.  In this case,
is it natural to use the branching technique to differentiate
the non-Mysql app to the MySQL app?   Or should I just
forget the branches and use a seperate repository?
I've got this feeling I'm 'abusing' the branch technique
in that I'm using it for a purpose that it isn't intended
to be used for.

Any clarifications appreciated.

Ed