Are we able to edit the adversary faction to represent a different faction entirely?
Yes, you can actually edit any faction if you wish to do so. In general, faction files are found in a mod folder's
data/world/factions directory, so you can start editing the Adversary faction or any other modded factions from there.
If, instead, you want the default Adversary star system to be occupied by an entirely different faction, just edit the
customStarSystems.json within the Adversary mod folder and replace all instances of "adversary" with the ID of the replacing faction.