#2
So are you talking about using a volume pedal in the loop so you cut the gain going into the power amp?

What are you trying to accomplish here? Are you just trying to cut some of the gain out of the lead channel while preserving your clean channel?

I have my Clean and Lead channels sounding completely different on my 5150 - I actually have a decent clean with some 5751 tube swaps, neck pickups, volume knob roll back, delay, and reverb so just cutting in (out) a volume pedal wouldn't work for what I do.
Guitars:
Jackson Kelly KE3 - MIJ (Distortion/Jazz)
Jackson DKMGT Dinky (EMG 81/85)
ESP E-II Eclipse Custom (JB/'59)
ESP LTD EC-1001FR (EMG 81/60)
Fender MIM Strat

Amps:
Mesa/Boogie Dual Rectifier Roadster 212
Laney IronHeart IRT-Studio
Peavey Vypyr 30
Peavey ReValver Amp Sims
TOOOO many T.C. Electronic Pedals. . .
#3
Though gain is affected by volume, a volume pedal is not a gain pedal.

My #1 pedal is my EB Jr, I use it a lot to get different tones.

I can say the amp can make a difference, for instance running the gain channel on an Orange vs the gain channel on a Sunn vs the gain channel on a Marshall...all of them had a different result with use of a volume pedal.

But those differences were subtle at best. At the end of the day you're running high gain (I presume with your 5150). Backing off the volume with a pedal will get you varying stages of crunch or dirty clean. And when I say dirty clean, I mean the dirty part. Once you've rolled it back quite a bit it also does some tone stuff (I'm not a nerd about it so I don't have fancy words)...basically it makes it sound a bit darker and lofi. I love that sound which is why I use a volume pedal a lot.

get a footswitch if you want cleans.