One way could be exporting lossless 16-bit TIFF or PNG from RT, in some wide colour space and without sharpening, and then doing relighting + final processing steps in another tool… However, if you want to apply a CLUT after relighting then yeah, tricky.
It would be great if RT supported something along the lines of “take the entire canvas after initial raw processing but before CLUT and final touches and put it into a temporary file; allow me to do something with it in any other tool; then load it back and apply the rest of the steps on top of that”, but that might require it to store that edited canvas somewhere in addition to .pp3 file.
Well, it’s not a roundtrip if you just feed the output to another tool. My processing script typically pushes RT-prepared PNG to something like ffmpeg which may do resizing and more, depending on the end format.
