Well, I just got done setting up my harnesses. I went to Home Depot and got a set of jeweler's screwdrivers.
The Metra harness was the easiest to work with: I inserted the 2.0mm screwdriver into the slit on top of the pin and pushed down. After a little tugging and maybe a little more pushing, I was able to remove the wire. To reinsert, what vetteguy said.
Since the Metra harness is missing the dimmer wire, I moved the brown "autotel" pin into the dimmer spot. The blue "elek ant" wire remained in the top row and was unused, so I removed it from the harness.
The Schosche reverse harness (MA03R) was a much bigger pain in the ass. Removing wires was easy: used a 1.4mm screwdriver (the smallest in the set) to push the tab above the pin, slid it out a bunch, then used a larger screwdriver to lift the middle piece in the harness, and after a little pulling, the wire left the harness.
Reinserting took me 1 hr to complete, though. I'm probably missing some big chunk of the puzzle and someone familiar with the Scosche harness voodoo will probably laugh at me, but ... I ended up taking off the front piece (as per Aydu), and then proceeded to use a 2mm screwdriver to ram out a bigger whole inside the two new wire locations. After a bunch of ramming, and reinsertion attempts, finally the wire slid thru the front. All this ramming was because I couldn't insert the wire from the front or the back without it, even while lifting the center piece and/or the little tabs above the pin holes.
The Scosche harness is missing wires in both illumination and dimmer locations; however, the power antenna wire is present. Thus, I only really needed to remove one wire off the second harness for dimmer, and I just relocated the power antenna wire for illumination. I did manage to break one of the wires/pins off the second harness... lesson: don't pull out pins/wires with your teeth, even if you're frustrated.
(In the reverse harness, replace all mention of "pins" with "pin jacks" or whatever)
End result:
1 x Metra harness: move 1 pin, remove 1 pin
2 x Schosche reverse harness: relocate 1 pin jack on 1st harness, move 1 pin jack from 2nd harness, break 1 pin jack/wire while doing so (optional

)
I took some pictures of the reverse harnesses before/after and the Metra harness after (forgot to take the "before" pic), but I'll put those up later once I'm done with the install.
Time to hook together all the wires except speaker wires and power on/accessory... just twisting them together and masking w/ electric tape should work, right?
[edit: grammar]