Anything's algorythmically possible. Just layers of complexity.

I don't expect you to be able to write a magic converter that does everything automatically, just a batcher such that you could have it replace hitplayer (etc) with triggeraction (etc), then do the rest manually. That should be possible, no? There are a lot of commands to remove, but one at a time...

I don't see how that makes it any simpler to implement what you requested.

Even when you do that, you need to add serverside parts to react to the trigger. And it's not simple to write a heuristic that would recognise all the different permutations of the player-searching algorithms needed to use hitplayer effectively.

Yes, everything is possible.
I remember when I tried to write my first version of the converter. It should parse the script and then it should try to move whole blocks to client-/serverside depending what commands they used. The problem was parsing the script. It isn't easy and I don't have the time for it. So it will be my simple converter which I hope to finish in a week, but which won't be able to convert 100-600 levels. :(
Replacing hitobjects with triggeraction? Why?

...*shrugs* I recall hearing hitobjects doesn't work in NPCServ is all.