PB 12.6 (build 3506) Application Exit Codes

Question

Environment:  Windos 2012 R2 Server,
PowerBuilder 12.6 Build 3506
Building 32 bit application
I've got a utility application that's running as a service.  We're using NSSM (the Non-Sucking Service Manager) to run the program.
NSSM can take actions depending on the exit code.
In earlier versions of PowerBuilder I could accomplish this by setting Message.LongParm in the application close or application system error event.
Now, that's not working and the advice I'm seeing tends more toward
// External FUNCTION declaration
SUBROUTINE ExitProcess(ulong uExitCode) LIBRARY "kernel32.dll"
// Powerscript
ExitProcess(50)
But that seems like it terminates the application and any clean up that might have occurred with a normal application exit isn't going to happen.
my question is...
Is this really my only option or is there some other way I have not been able to find?
Secondary concern.. where do I find the full 12.6 manuals?  I keep ending up at SyBooks which only has documentation up to 12.0 and SAP PowerBuilder 12.6 – SAP Help Portal Page only gives me the new feature guide, installation and release notes, but not the actual documentation.

Answer 1

I am sorry if I somehow led you to think NSSM is the problem.  It's not, PowerBuilder is.
The PROBLEM restated for clarity:
In earlier versions of PowerBuilder I could add code to the application close event that set Message.LongParm to a value and then that value would be accessible to a command file via the ERORLEVEL system variable.
In my current tests with PowerBuilder 12.6, setting Message.LongParm is not working so I Googled the problem and the advice I'm seeing tends more toward using:
// External FUNCTION declaration
SUBROUTINE ExitProcess(ulong uExitCode) LIBRARY "kernel32.dll"
// Powerscript
ExitProcess(<Value>)
But that seems like it terminates the application and any clean up that might have occurred with a normal application exit isn't going to happen.  That's not ideal.
My Question is:
Is there any method exiting that will allow me to set that system ERRORLEVEL variable that does not require my causing an abnormal termination to my application?
Or is using the external function ExitProcess really my only option?