I haven't actually tried making a ReBlast, but here are my thoughts. Please keep in mind this is just based on eyeballing a Blast (without taking it apart) and using some of the tools in my parts stash for comparison.
Will the Rebar plier head fit with the standard Blast tool configuration?
The plier head should fit just fine, but looking at the tool loadout, I'm guessing that the scissors and possibly the small flat driver on the Blast will prevent the tool from closing fully with the Rebar plier head installed.
Can I swap the Blasts small bit driver with the Rebar's awl without issue?
The small bit driver is slightly thinner than the awl, but there is also a lanyard ring on that side of the Blast that you could remove to make some extra space to accommodate the awl.
Lastly does anyone make a tool like a little socket to unscrew Leathermans?
sadly, these are not commercially available. someone here made a set of their own in the past using a vise and a cheapo socket set, but my search skills are failing me at the moment, so I can't find the link.
hope this helps!
let us know how the ReBlast turns out.