If you want to dynamically install and remove event handlers:
Put the plug-in in a non-standard location (a location where Softimage does not look for self-installing plug-ins).
Use LoadPlugin or LoadPlugin and UnloadPlugin or UnloadPlugin to load and unload the event handler as required.
Except where otherwise noted, this work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License