would mixing some type of flavoring ingredient like crystal light with peptopro decrease it's absorption rate or make it less effective?
That's a big N-O. Something with other protein or fat in it would though.
I think you'll be fine mixing in some crystal light. I personally put half a scoop of Surge Recovery in with my PeptoPro to augment all the nastiness... Man I can't wait for Anaconda and MAG-10 to get here.
Mixing it with diet arizona green tea makes it awesome for the fruit punch flavor at least.