It's possible, but it's not simple. how do account numbers get populated, and then used in other tables? This entire process has to change if you are going to re-use the "account number" table you currently have for another purpose and move the actual values somewhere else.

Encryption can help, but you really have to think about who can access the information and how, and how you can change your code for the decryption.

Right now, you aren't going to solve this in a forum. It's a major change and an architectural change as well. It also sounds like you don't have enough knowledge to design this. It seems obvious to me what problems you have, but it's a lot of work to explain them and detail them. That's the type of work I would want to be paid to do. If you don't see the issues, then you aren't really ready to tackle this by yourself.