Bass through guitar amp?

This is also something I'd like to know. But I really don't think it would work, given the different frequencies and the lower tones of a bass. Maybe if you tweaked the EQ a certain way?

I've played basses through guitar amps many times, and found that, overall the sound isn't all that great, but not that bad. I mean, you can't just plug in, crank it up and expect it to sound GOOD good..It does work though, and I don't really see why it'd damage it all that much, if at all.
But it won't sound like a bass amp :)

set the treble to 5, bass to 10, mids to 0, and try it out

i wouldnt recommend it. It may damage it (in fact it will if turned up loud enough). Just be careful. Keep the volume way down. Definately wont be able to play it with anyone else. I would just not do it period if I were you. Maybe try to plug into a stereo system. Even then dont turn up too loud.

As it turns out, putting mids at zero, cranking the highs, and putting the bass a little below twelve o'clock and adding a very slight flangeish delay will give a wonderful slap tone.

As I said, don't crank it up. It won't hurt anything to just play around on it.
It sure as hell beats playing on it without an amp.

...or, at the very worst, it will give you a chance to try out a new speaker or get a fascinating (read "broken in") new blues tone from the old one!

It's very unlikely that you can damage the built-in speaker of any combo guitar amp by playing a bass through it. The only way you can tear a speaker up is if the amp has sufficient power at the bass frequencies in the octave below the guitar's low notes to tear the cone by pushing the voice coil assembly past its usual "throw." Modern speakers are made with surrounds that tighten up and stop the cone's travel (resulting in distortion) before they can go too far unless they're driven with more power than the speaker's rated for. At the same time, few guitar amp speakers have a bass resonant frequency lower than about 70 Hz (which is about the low D in Drop D or Open D tuning), and below resonance speakers become extraordinarily inefficient, sucking up audio power but not moving the cone commensurately. Yeah, if you hook a guitar speaker cab up to a 400W bass amp you can tear it to pieces in a hurry. But not a guitar combo with a bass played through it. The speaker's already built to handle all the power the amp can put out, and below its resonant frequency it'll just sound weak, farty and muddy.