Jenkins Integration - Command Line Argument

I don't understand the problem, but since you are assigning the variable inside a function, why don't you just add an "if" to check if that last parameter contains the string JenkinsTCPlugin, and if it does then you pick the previous parameter? That way it would not conflict with your PowerShell scripts. 

Another option is to add a Project Variable in TestComplete to reference your environment.

That way you can pass the environment via the CLI parameter /pv:myEnvironment=QA or /pv:myEnvironment=AT, or whatever.

Then in your script you just reference that variable doing Project.Variables.myEnvironment, and it will pick either the value you set up as default on the tool, or the value passed as parameter through the CLI and it won't matter in which "position" it is