Is there a way I can manually update client side contents after sign-up

I’m a front end dev on my way to backend and this is a personal project. It was meant to be static so all users see the same information on their page but now I want to be able to change some details based on the clients who signs up. For example. All users were meant to see a $20 bill for a community project but now I want to be able to increase or decrease that amount on different client user page.