Storing reference to previous string (OSC message)

Trying to translate basic coding logic into BP in a OSC server.
I am generating 2 messages at the same time from a radio button, the new and the old. This from the older mk1 version of the TouchOSC app which uses toggles for radio buttons.

I need to only respond to the new string, so I need to store a reference to the old and compare against that for every message received so I can ignore the old.

Where I am stuck is how to save a reference to the previous string . Thinking in code I need to store this as a class private var.