Confirm there are not already settings or features that do what the shop is asking for: I have checked and there is no setting/option to change the ‘Register’ word to ‘Join Now’ or other words.

What does the shop want the product to do: Shop want to 'Register' Reply/Comment word to any other word because the suspension happened after a customer used the word "register," it's very possible that Facebook has strict restrictions around that specific term for sellers, causing it to trigger an automatic violation.

Why/how would it improve sales or efficiency: If shops have the option to change/edit ‘Register’ word with any other word then they will not get any violation or it will not lead to FB account suspension. If a shop 's FB account will get violation or suspension then it will impact their sales and they can’t post or go live on FB.