Apparent Solution (pilot errors in OP by a Theater View newbie

)
(1) Standard View: The entry in
View Tab (or RMB Tree Item) > Customize View > Show Categories in this order > Edit > Category > "Expression to display ..." appears in the left pane Organization Tree for each Category. Thumbnail Text is entered separately per Category from the respective View Tab dropdown menu.
(2) Theater View: The entry in
Options > Theater View > Details > Edit > Category "Expression to display ..." appears as Thumbnail Text (there is no left pane Organization Tree visible in this View!). There is no separate Thumbnail Text entry.
Therefore, to show the equivalent of Standard View Custom Thumbnail Text in Theater View, it is
always necessary to manually enter/edit the custom expression in Theater View's
Edit > Category > "Expression to display".
The
...Add... command referenced in my OP works correctly, as is, to transfer all Categories (but does not transfer custom Thumbnail text).
Suggestion: Add a few words to the popup menus
... Edit > Category > "Expression to display" to clarify
where the expressions will show. Example: For (1) "Expression to display in Organization Tree ..." For (2), "Expression to display under Thumbnail ..." (see attachment). As is, these menus appear virtually identical, yet implement very different end results depending on context (the menu is "overloaded") - a prescription for customer confusion.
5/14/2025 Minor edits to clarify.