Saving handles as strings (not 3DGS strings), and reading them back in or resurrecting them again (via C / C++ file IO), in compliment with the 3DGS load / save instructions (in C-Script), seems to work as expected using a C++ interface and the 3DGS plugin SDK. This seemed to work well enough when I implemented load / save functionality for my entity lists eLL plugin (C file IO) and later for the newer version, el (C++ file stream classes IO) plugin.