replacing colors exactly in gimp?

i’m making a weapon for a video game and there are 2 teams, red and blue. some weapons are red on red team and blue on blue team. some weapons have brush strokes on them to make them stand out more. but i need to know how to have all reds turn to blue exactly.

heres the red team version, but i also need a blue team version, so i use the color exchange tool to change both the base red and the brush stroke red, which is slightly darker than the base color.

as you can see, some of the areas are still red. i can always manually edit it to make them blue, but i need it to be perfect. i see people all the time making blue versions of red weapons and they are all red and blue without any difference in the texture besides the changed color. how do i change every red color to blue exactly and without any mistakes?

also sorry if this isnt the right site for this question. i cant find any other gimp support forum thats active.

colors->hue-saturation->fiddle w/hue

thanks. this helped a lot.