Here is the response from Nemesys, when I submitted the question to their technical support team. Hope this helps.
Actually, unless the file uses some new 2.0 features (4 stereo layers instead of 2, or Amp and filter LFO) they will simply load into the GigaSampler. No need to convert them back. They are backward compatible. Even the ones that use the new features will load but simply ignore the extras. To convert to 1.0 would involve loading it in the editor and saving it.
Hope this helps
Dave of NemeSys