No regex required -- you can treat the "old" address as an array, delimited by the @ symbol. I've used a variable for testing, but you could just as easily operate on the System Clipboard:
@Nige_S is right – this one doesn't require a regular expression, and a solution was easily within your grasp. Plain old, ordinary string-replacement – plus knowing how variables and strings concatenate in text variable assignment actions.
Mark Nige's solution well – that technique is very useful for a variety of things – and will be more so when Peter gets around to adding EOL characters to the possible delimiter strings.
Here's the regex just for fun – regex will nearly always be my go-to method for doing this sort of job, because I've used it continuously for nearly 30 years now.
