Can I jumper across amp speaker outs to a 2nd amp's spkr outs?

"Can I jumper across from one  amp''s speaker outs to a second amp's speaker outs if I only power up one amp at a time?"

Yes, if:

1) amps have protection circuits with open contact relays if amp is OFF

2) neither of amps is in bridging-balanced mode

3) fool-safe ensuring of turning both amps the same time ON! Two amps turned ON can be disastrous! 

Speaker switch (can be used both ways, to work as amp switch) sounds more reasonable, safe solution! 

@westcoastaudiophile 

You're not wrong, technically; but it's like saying you can drive home drunk if you take side streets and go slow.

plombier, technically, your response, to not your question, indicates you are saying I am right? LOL  

westcoastaudiophile, I'm not saying you're not right, but a selector switch is still the right way to go