Brenda,

PK is primary key. You are facing a problem right now because your primary key on the customer table is meaningful to people and now they want to change its value. You can either do all the work to change the value in all the tables now or you can fixed the problem and make the "customer number" NOT be the primary key to the customer table.

Either way you have work to do, one way you put a bandaid on the problem until it arises again, the other way you fix the problem so it won't arise again.