hello  out there,
i wonder if there is a short way to slice a quarter-note with one click into four 16-notes in the pianoroll editor?
thank you
 

You can't create four simultaneous splits with one click, but the following works.
 
1. Set quantize to 1/16th notes in the PRV.
2.. Hold Alt with the Smart Tool, and it turns into a scissors tool that splits with a click
 
Because of the quantization, just click somewhere close to where you want the split - quantization will make it exact.