I think the ReGroove Mixer is cool, how it can add more human like timing irregularities into drum patterns.

My question is this. Should this be done before doing a complete arrangement, or can it be adjusted after a complete arrangement?

In other words, if I adjust the drum patterns with the ReGroove mixer after creating an arrangement, does it just alter the drum patterns, or does it correspondingly alter all the other instrument tracks as well, in order to keep time with the newly altered drum sequence?

Hey,

Regroove only effects the tracks that you have assigned the pattern too. I don't think it really matters when you use it.
You may want to change the rhythm of the drums to suit a melody you have just written or you may want to write the moldy after using the re-groove. My preference is to get the groove of the track done first. But i do it both ways.

My biggest problem with regroove is that you have to copy the pattern to track, you can't change the groove of a drum loop in the pattern lane.

To get a more human feel is all about tweaking the settings, I can't really help you there, as it's dependant on your drum pattern and tempo.