Im writing extension to motion simulation module. I haven't make it working yet, but i found usefull information in documentation of programming tools and samples.
For this task i recomend topics:
NX Open -> Execution methods -> Adding custom Applications
Menuscript User's guide -> Menu Files
Menuscript User's guide -> Directories & Environment Variables
And sample: MenuBarDotNetApp.
This sample code is about custom NX app (like drafting or modeling), how to have button to switch to this app and customise avilable menu buttons in custom app.
Hope that helps.