Follow-up:
I tried to override the "rename files from properties" behavior that converts a blank/0 [Rating] into path/filename text "_stars" rather than "0", by using the Replace function.
My Directories rule expression contains this (in a more complex expression): Replace([Rating],_stars,0)
However, when applied to a file that has a Rating of 0 but a folder named "_stars", MC tells me "no change".
Maybe MC's Rename tool sees "_stars" and "0" as equal; why?
Or maybe the value-to-text conversion happens later in the process, beyond user control. Perhaps the database stores "0" for a blank Rating, but the Rename process, AFTER applying any user expressions (such as Replace), then converts a Rating of "0" to "_stars". If this is what's happening, it seems arbitrary and undesirable.
Can anyone clarify what's happening? Is there a sure-fire way to do this?
I still think that a Rating of 0/blank should result in "0" when using [Rating] in Rename, just as a Rating of 1 results in "1", etc.
But a strong second choice is to respect the user's entire Rename expression, and not override it behind the curtain. (With the exception of not allowing "illegal" filename characters.)