Thanks Dave, I am going to give it a try.

"Dave O" wrote:

This formula did it for me:
=IF(NOT(ISERROR(FIND("0000",A1,1))),MID(A1,1,FIND( "0000",A1,1)-1)&"1135"&MID(A1,FIND("0000",A1,1)+4,LEN(A1)),A1)

This evaluates the entry in cell A1. If it finds a series of four
zeroes it parses the entry and replaces the four zeros with 1135. If
four consecutive zeroes are not found, it returns the value in A1.

Is it possible that 2 separate strings of four zeroes may appear? If
yes you'll need to run a similar formula on your *new* entries, as
well.