JPG editor that allows you to transform one RGB value into another?

Say the RGB value of an area on a JPG is 128, 192, 128. Is there a
program that would allow me to transform the color of this area into
any other RGB value I wanted (say, 0, 192, 0)?

You want a color replacer function. It has nothing to
do with JPG specifically. It's just a function that's
avaiable in most fullscale image editors.

> Say the RGB value of an area on a JPG is 128, 192, 128. Is there a
> program that would allow me to transform the color of this area into
> any other RGB value I wanted (say, 0, 192, 0)?