<stuff about other software removed to avoid confusing people>
Sorry for posting so many questions 
You can use DOpusRT.exe to send commands to Opus. You don't have to resort to low-level (and dangerous, if you get things wrong) implementation details like WM_COPYDATA.
DOpusRT.exe documentation is here:
https://www.gpsoft.com.au/help/opus12/index.html#!Documents/DOpusRT_Reference.htm
If you have questions, please just tell us what you want to do, rather than how you would do it in another program. Those details will just confuse the issue, or other people trying to find information about Opus if they don't realise it's about another program.
I've seen these, it might be better if the script can be run without the full path to dopusrt.exe.
It doesn't really matter to me.
You can get the full path to a process easily enough via its window handle. This is still better than using WM_COPYDATA with the same window handle.
(You can also get the path from the registry, but that won't work with portable installs, if you care about those.)
Ok thanks, I like portable software. I just get the script from somewhere else and edit it. . .