didn't know that tool existed in GIMP
but then again, I don't use GIMP
if I wanted to recolor something to a specific color, I'd
- check the RGB value of the color of the thing I'm trying to recolor
- compare it to the RGB value of the color I'm trying to recolor the thing with
- find the difference between said RGB values
- set that as my color on the brush on Krita
- create a new layer set to "Color" mode/set my brush mode to "Color"
- paint over the entire thing/use the fill bucket tool
so it's just like your method with added steps