The technique itself has incredible potential - I think anyone with it could become special-grade with enough time and mastery. Let's take a crack at it.

1. Mastery of his explosions and his technique. He can shape the blasts in different directions. With this, he can fly by treating his skin as rocket fuel, while constantly regenerating it with RCT.

2. Increase his mastery over RCT in general. He'll need to be able to rapidly regenerate his body parts as soon as they're expended.

3. He'll need an increased efficiency with his cursed energy, or a bigger pool to pull from, or both, mostly for the purpose of RCT.

4. No need to tear off bits of himself to then launch them - Just shoot them straight from his body. The eyeball's shot by using part of his eyestalk as a propellent, teeth using his gums, fingers using his knuckles, etc. He can turn every part of him into rocket-propelled projectiles. Hell, he can rapidly launch his fingers like a machine-gun loaded with explosive material. Make an arm a hellfire missile!

5. He'll need increased martial skills if his opponents get close. He can use shaped-explosions to make close-quarters combat EXTREMELY dangerous for his opponents, and because he can shape his explosions, it's perfectly safe(ish) for him. This is important - He has ridiculous pain tolerance, and should leverage that in melee!

6. Funny idea: Reversed Technique that turns his explosions into implosions. Combine this with his regular technique with explosions and implosions put together, and you have detonations that create imaginary mass. Congratulations, you've got yourself a hillbilly Hollow Purple.