Yes, post cutting is normal, but you can't cut the same action twice. If the first time fails, that's all you get. Either take the hit or get out of the way.

You should also keep in mind that Max's character is himself superhuman. Those thrown weapons aren't going to be moving at normal human speeds. Depending on how strong and fast he is exactly, they could easily be moving as fast as some bullets, which would give Rauchnaut considerably less time to make his moves than if he were fighting even an Olympic level human.

Edit: Regarding my first statement, that's in the case of similar level opponents. If one character is tremendously faster (on the scale of Mach 1 vs peak human) then they could obviously get more than one attack in between their opponent's strikes. Though even then, taking a whole post for every attack isn't the way to go. A post it should be entirely self-contained, regardless of how many attacks are in it.

And in regards to you altering Rauchnauts attack, yes, a change that drastic needs to at least be hinted at beforehand, otherwise you can simply say he was planning for anything your opponent comes up with as justification to pull any move you want, regardless of whether or not it was originally intended.