Hi Gms9810, well in your way you have taught me something about the brush editor. I checked brushes in the brushes dialog with the editor and they are all Read-Only, even ones I made. I don't think I've ever tried to edit a brush from the editor and, logically, you should be able to, but you can't.
This is what the Gimp Manual says about the brush editor.
Quote:
The Brush Editor allows you either to view the brush parameters of a brush supplied by GIMP, and you can't change them, or to create a custom brush from a geometrical shape, a circle, a square, a diamond.
Instead, open the Brushes dialog by pressing Ctrl + Shift + B on your keyboard. Right-click the brush you want to edit and choose Open Brush as Image. Then you can edit it.
There, now we've both learned.
![High 5 :hi5](./images/smilies/hi5.gif)