Just so you know, lawlegacy, that Radiant will only give their SDK to "approved" vendors. This is extremely difficult to get even for established development houses, so the odds that you will get this are precisely zero.
You may want to explore the possiblility of editing 'grind' files. Grind files are multiple dbf files that are created to feed data into the reports so that you can view sales data, etc. You shouldn't really edit these files, as they can easily be re-written by the application, but to read data and import it into another database, for example, can be useful and is a fairly common practice.
But to write to a translog is a 'no-no'. The IRS will staple you to a cactus in Nevada, and Radiant will lose all certifications and reputation (what's left of it).
Also, may I ask what your role is? Are you a restaurant owner, a developer, or ????
All I can really tell is that you somehow got your hands on a POS system.
It would help me to address some of these issues differently.