Can I normalize max pixel intensity of one image to another image?

[Piranha91]

I'm using gimp to apply freckle textures to a face texture for a video game. All textures are other peoples' work; I'm just pasting the freckles as a new layer onto the face and colorizing them. This is my first exposure to GIMP. I noticed that the face freckle texture is lighter than the neck freckle texture. As a result, when colorized to the same HTML value and applied to the character model, the neck freckles are much darker than the rest (example). Since the original freckle textures as greyscale, is there a way to normalize the max pixel intensity of the neck freckle texture to that of the face, so that they come out to a balanced intensity?