I have it working now in both part and assembly mode. The same mapkey "imdi" is invoked in both modes and it runs so far. So for you GUI fans if you imbed this in a ribbon tab you will have a measure that will report the deltas with an icon pick plus 2 refs.
Caveats: The active model (.prt, or .asm) has a Csys with a tag containing string "CS0". In my start assemblies it is ACS0 so I modified the search parameters to search names using "*CS0" which captures both. It seems to be pretty robust using this approach.
I had to record a separate search in assembly mode to find the CSYS of interest due to the inclusion of submodels tab in the search dialogue defaulting to yes. That is the mapkey ".acso" which uses nested ".ics0" created to work in part mode.
Let me know if you break it or see a better way to do this. I have enclosed the mapkeys in the txt file here.
