I edited the question to clarify what the team needs to do: When using "Apply Gloss Everywhere," is there a way to add a ruby gloss to only OT books?
When I tested it, the gloss was added to both the OT and the NT. I did get the green banner stating information about the number of times the gloss was added, information about how many books were affected by the gloss that was added, and an Undo link.
The team would like to specify that the gloss be added only to the OT books.