Our old sales manager had a habit of creating a new customer code every time a customer asked for a product to be shipped to a different location.  So to find out how much cust X purchased you have to run xxxx1 to xxx5 (if only it were that easy, there is no rhyme or reason to the name code he created)
 
 The problem is that this years Top Customer bought nothing last year - due to the new cust code he created.  I was thinking that I could go in and globally change the customer codes...
Globally replacing anything freaks out my IT friend.
 
Any suggestions on how to merge the data?

Thank you Lynn!  That is great news