I haven't tried to run a non-Sandboxie session and a Sandboxie session simultaneously. But AFAIK, there's no danger if the user does not actually change anything in the SB instance.
AFAIK, here's how the process works.
The non-SB EN uses all the normal files.
When the SB EN starts life, all the current non-SB files are copied within the SB. After that, the files lead independent lives.
If the user does not cause any files to be changed within the SB, the SB session can be closed at any time with no effect on the non-SB files.
Assume that the user causes some files to be changed within SB. When the user closes the SB session, she is presented with a list of files that have changed during the session. She can then choose which of those files will overwrite the current non-SB files. IMHO, the safest options are either (a) to overwrite no files, or (b) to overwrite all changed files. In both cases, the result will be a consistent database, with no conflicts.
Obviously option (a) would be chosen by the OP.
Good point ?
But, IMHO, the situation is no different to having one instance on your laptop and one instance on your phone. I admit that no-one is likely to make changes on both of these devices simultaneously.
I'll run this suggestion past the SB forum, and get their opinions.
Thanks.