How can I add/alter wiring inside single-brick walls?
I highly recommend using Wiremold for this kind of project, but it depends on the aesthetics that you are going for. 1/2" EMT when bent properly gives a really neat look on exposed brick. Using a pipe bender takes a bit of skill and practice, but can be an art form on it's own.

I really don't like the idea of channeling into brick (or block) because:


It never looks the same again, even when you paint it
It weakens interior walls, which might be more prone to crumbling / falling in an earthquake prone region than they otherwise would.


500 series Wiremold should be all you need to do the job.