Extremis is not a virus, per se.
...It wouldn't make him stronger... it might make him a lot weaker. An Extremis enhancile is basically a Hyper-Zoanoid who doesn't change form. Although a very strong one: faster than Thancrus, easily as strong and tough as Derzerb and with his flame breath too, electric powers like Elegen... and healing as fast as the Guyver from anything that isn't fatal.
But if Guyot was as tough as a Guyver in human form... well, it's no telling what Archanfel is capable of. He always uses energy attacks, or psychokinesis. Who knows? He could easily be as strong as an Extremis enhancile now.
And his anatomy is radically different, I should think. This could well be a downgrade, provided he even survives the process! On the other hand: if it works, he probably wouldn't have to hibernate anymore.
...
I read 'Archanfel' for 'Aptom'.
I don't think Extremis could affect Aptom at all.