#1
This may sound a bit dumb but can a foot-switch designed for one amp be used with a completely different amp? I thought about it and thought it most likely couldn't but would be most grateful for a definitive answer.
Gear:
Fender American Tele (Lefty)
Squier Affinity Strat (Lefty)
Boss DS-1
EHX Small Clone
Fender Hot Rod Deluxe
Laney LG12
Danelectro FAB Flanger (Rubbish)
#2
The answer is sometimes. Many footswitches are simple and usuable on different amps. But some are not. I bought a f/s on eBay for my Super Champ XD. It was a Fender and looked like it would work. However the circuit inside had a small difference. Fortunately I could see the difference when comparing to the correct footswitch and mod it to work.

If it's as simple as a single switch just changing channels then it's likely that is will work. But switches with TRS (stereo jack) connectors may have more complex circuits.
#3
Ah thank you for the clarification.
Gear:
Fender American Tele (Lefty)
Squier Affinity Strat (Lefty)
Boss DS-1
EHX Small Clone
Fender Hot Rod Deluxe
Laney LG12
Danelectro FAB Flanger (Rubbish)
#4
Most reverb footswitches are exactly the same, I made one which cost me nothing and it works on four amps so far.
..I was watching my death.