I would like to create a custom tag and update it from the client side, but I want to capture all the devices that have selected older versions as well.
I know I can use multiple 'iOS App Version' tags to target multiple previous versions, but I would like to group them together since we do frequent updates and I want to provide a better way for our marketing folk to send out push notifications.
Is it possible to select devices with particular 'iOS App Version' tag values and add the custom tag to their record in the UA database?
Segments are a great way to group together different pieces of metadata such as tags or locations. You could create a segment with the different 'iOS App Versions' you are trying to target and send push notifications to that segment. You could even attach tags to those push notifications that could then be added to devices depending on the user response (i.e. user presses 'yes' button in the notification, tag "interested-user" gets added to their device).
I hope this helps!