@Esteban_M
Scripts don't enters values in windows for you. It works at the source, by modifying the elements properties directly.
There is a lot of scripts involving notes velocity, JSFX for effects or Lua for offline processing.
Here is template I made in Lua, which process selected notes in MIDI Editor:
https://github.com/ReaTeam/ReaScript...I%20editor.lua
You only have to add your own math in the middle.
But if you do that everytime for certain tracks, I will advice you to use a track FX insert, so that you just set it once and forget it.