Menu files are only read when you start NX, there is no other way.
If the menu file is specific to an application, modeling, drafting, manufacturing, etc., then it is read at the start of the application.
Production: NX10.0.3, VERICUT 8.1, FBM, MRL 3.1.7 | TcUA 10.1 MP7 Patch 0 (10.1.7.0) | TcVis 10.1
Development: VB.NET, Tcl/Tk Testing: NX12.0 Preparing: NX12.0
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