For the NAS it is necessary to have a trigger (method) with ID 99. In my system that function exists already (NASHandler), but how would it be possible to create it with a specific ID? I can obviously see the ID in a text-export, but change or specify it?
When designing the Codeunit, choose C/AL Globals from the View menu, select the Functions sheet and create a new function, then - again from the View menu - choose Properties: voilá.
You should not change any ID of any function, nor add any function to the CU1 in Navision. But you can use the NASHandler function to call your own CU by adding some code.