If I load it or unload it from the task bar or desktop, it works fine. If however, I load it from a command button in DirOpus, it won't unload, but remains in memory -- however many times I run it, there will be an instance in memory.
Is there a way in the DO command set to make sure the program has unloaded?
Opus is just launching Everything.exe and passing it whichever arguments you specify; what Everything does and which command line arguments it needs are unrelated to Opus.
Maybe someone here will happen to know the answer but doesn't Everything have a support forum where you could ask?
There are more modern alternatives out there, including Windows Search, which seems to have moved on since the folks behind Everywhere wrote about it, and which Dopus can plug into. Just work out how to configure it.