Answering my own q and sharing in case it helps anyone: The problem was a glitch where Additional Attributes refused to save. This is a Loadrunner known issue covered here: https://portal.microfocus.com/s/article/KM000018481?language=en_US

Commenting out the line mentioned in the article failed and caused a JS error while loading the Additional Attributes page, but commenting and then uncommenting it restored functionality and re-enabled saving changes.