Need to re-render every time I change something in the compositor because of full sample Not long ago I have discovered the full sample feature on Blender.
The feature is great and helps a lot. The problem is that whenever I render a frame with Full sample, the image is anti-aliased, but if I change something in the compositor, the image becomes aliased and remain jagged unless I render the entire frame. It is slowing me down because sometimes it takes several hours for a frame to render. Is it just like that, is there any way to avoid re rendering? 
Thank you!
One simple, however not ideal, is to save the final render to an external file; then loading it up and applying the composite to that.

I would recommend using a multilayer OpenEXR file; these however take up quite a lot of disk space.