Thank you very much for the answers!
m_nNextThinkTick 1 or -1 does nothing for me.
Blodia's method does work on hegrenade_projectile perfectly. Both methods perform just fine.
Unfortunately, it seems to be doing nothing to a decoy_projectile, nothing at all.
I would prefer a SDKCall even tho it might break after an update. Even better, i would love to learn how to find that kind of stuff myself. My knowledge pretty much ends up on virtual functions, and it didn't help me