I did try just using Exitus-1, the reagent. It said it injected it, but nothing else happened. I mean, if it was that easy why find 10 other reagents? I don't think I'm understanding you here.
Edit: I looked at the wiki and it said to do what I already tried: making a copy of Exitus-1 and injecting that. Again, no feedback from the combinator on if I did anything right. Do I need to put both the existing Exitus-1 AND my own Exitus-1? This is super confusing and non-intuitive. Is there any feedback if you get it right, or do you have to go confront the boss to see if it worked?
Edit edit: OK, so THIS time, when I put Exitus-1 in there, it said prohibited. The first time I tried it, it let me do it. I'm now thinking that was a bug. For some reason, now that I've fiddled with the combinator a bit, the glitch is fixed? Help me out here people.