The hex values for the planets is located in the file 'SYSTEMSD.dat' in the GData folder in your SWRebellion folder. The hex values for the sectors is located in the file 'SECTORSD.dat'. To get the hex locations(this process is tedious), make a back-up copy of your SYSTEMSD.dat, edit one value of the Systems option in RebEd, save it, then compare the original SYSTEMS.dat and the back-up copy you made. The systems are in alpabetical order and are grouped by sector. Meaning, you would see Coruscant and Balmorra in the same area of the file. You'll start to recognize patterns, where a new system starts, where it ends, etc.