If you want to add/change file in each user’s profile, then you need to run PSADT in the SYSTEM context.
If you need to read each user’s Environment variables, then you will need ActiveSetup to do that.
Active setup is a way to trigger a script or an EXE when the user logs on. PSADT can setup your standalone script or EXE to be triggered by ActiveSetup.
BTW: There are 3 different ways to do changes in user profiles: Installing in user profiles - ActiveSetup vs. Execute-ProcessAsUser