Is it possible to write/created effect plugins within Halion script?

Is it possible to make VST type plugins within Halion? For instance, a dynamics compressor on a Halion made drum instrument?

You can create midi plugins but not audio.

So, are there any utilities to include effects in Halion created instruments? is there a base set of effects? ie, could I have 4 knobs for 4 different impulse response convolutions?

Technically you can if you use the audio input feature.