To launch editor wtite "BrushEditor()" in the console.
Currently avilable tools: Square, Filled square, point.
To use Square or Filled square press to select first point and press again to selcet second point.
RMB - Erase
LMB - Draw
You can find saved brushes in the folder "Brushes" in the tpt directory.
After saving restart tpt and you can now select your brush using Tab key.
Demo:
How do I delete a brush that I made? I can't find the tpt directory