Welcome to your first FHUG posting Peter.
Sorry, but I have split your posting away from
Plugins planned/in progress (19399) and New Wish List Requests and moved it to the FH General Usage forum because what you request is already a feature of FH Place records, and has been since they were introduced in FH v6.
A Place record for Salisbury, Rhodesia can also have a Standardized place name of Harare, Zimbabwe.
That feature is provided because innumerable places have changed their name over time.
So a simple list of Place records in the Records Window will show both old and new place names.
It should also be possible to adjust the narrative Sentence Templates to mention both old and new names.
Also, see FHUG Knowledge Base advice
Working with Places and Addresses.
When you have digested that, we can explain how to alter your Sentence Templates by adding:
{=CombineText(" (now ",%FACT.PLAC>STAN%,")",)}