What are the effects of updating Subcustomer ID format? Is there any other way to show the parent?

Some of our users want to see the entity records in Parent Customer : Customer format rather than the current CUSTID - Customer format. This is for the big header on the customer page. I asked NS support about this, and they indicated that I need to go to Set Up Auto-Generated Numbers > check "WITHIN PARENT GROUP" box next to Subcustomer. To update the existing records they also indicated that I need to check the UPDATE box. If I do this, am I effectively overwriting customerid fields of all customer records who is a subcustomer? We have some integrations in place and they might rely on customerid field. While I want to fix something visual I don't want to cause disruptions. To which extend does this update change things behind the scene? Are there any other ways to show parent customer in big fonts on the customer page? Thank you for your feedback.