The last time I checked the gamma corrector simply gave you LUT:s to store your mapping values. It's not really a computed transformation so a lack of resolution doesn't apply. You simply exchange values to something else. Rather, you could see this as replacing the last gamma step in your previous chain.
By the way, I don't think you can add/subtrac from gamma without being in non-linear space. The TV/display is going to assume to degamma in non-linear space anyway for further image/color manipulations. If you change gamma in linear space you won't have the desired effect I would think.
Scaling and other video processing of course, in linear space.