In Trello, is there a way to search and replace text across all cards in a given list?
Trello doesn't provide "search and replace" functionality. Best you can do is use the API to find the relevant cards:
...then loop through the results, calling e.g. https://developers.trello.com/advanced-reference/card#put-1-cards-card-id-or-shortlink-desc to update the description. You'd need to do the same for whichever fields you wanted to update.