45 Ohm volume control on 8 ohm speaker, what would happen?
If you wire it just as a variable resistance, the volume will be low until you turn it nearly all the way to low resistance.

By adding high resistance, you reduce the damping the amplifier can provide to the speakers -- this may affect the frequency response (you may get some small amount of peaking at the speaker's natural resonance).

It won't damage your amplifier or speakers -- amplifiers are designed to be able to operate with light or no loads which is what this does.

If it is a high power amplifier (more than a few W), then likely high volume will damage your potentiometer (volume control) by forcing it to dissipate too much power.