Finally have a relatively simple system figured out to have a Collection of local images be mirrored / synced on Smugmug automatically (somewhat, anyway...).
Have it working like this:
Photo is added to LR "Collection"
Smugmug module has a "Smart Collection" set up to pick up certain files from the basic LR Collection above.
On Smugmug, deletions and additions to the Collection in LR are reflected normally (after clicking "publish", when deletions or additions are made...)
But if I crop one of the images in the collection, the cropped version never shows up in Smugmug. The same uncropped version remains.
Yes - I did "publish" in the Smugmug panel after the crop in LR (even though it didn't show as needing publishing).
The photo shows as cropped everywhere in LR - I just cropped it and clicked "Done". Is there something else that needs to be done in order for it to be recognized as "modified", and needing a re-publish?