Sure, it's ok to reduce levels. Will it change your mix? Ya, it might. If it does then you just deal with it.

It should be okay, but be careful if you're using compression on your Master Fader. If you hit it less, you'll have to adjust threshold and other parameters accordingly...

You want to pay attention to aux sends on separate tracks:
-lower the volume and there's less signal going to reverb or delays, it might change the sound a bit...
-if you have aux sends in pre, it's gonna be even worse, you could change the dry/effect signal ratio even more.

If you really really really want to make sure it sounds the same, rerecord your mix into Pro Tools the way it is right now, make necessary adjustments so that your session doesn't look like a christmas tree anymore and then compare the two mixes...
I do it all the time, sometimes I can't get the same mix, but you might find yourself very happy with a new version, peakless...

Thomas

Throw a peak limiter across the main bus just to catch the redliners. It's doubtful that it will change the sound of the mix.