Changing a Long Lived Topic

Your customer-profiles topic holds one profile for each of 4 million customers. It is compacted, six services read it, and some of those profiles were written years ago and never changed. The profile team now wants to change what a profile contains. How do you change the format of a topic whose records are never deleted by age?

On a topic with 7 days of retention, the answer is to wait: once the producer writes only the new format, the old format is gone a week later. A compacted topic does not work that way