Are there any examples of an update query that can search a field for a set of characters and replace only those characters? EG "ABC1234" change all BC to DE.

Depending upon your dbms, try looking for a REPLACE() function.

It might look something like this:

UPDATE TABLE1
SET COL1 = REPLACE(COL1,'BC','DE')
WHERE ...

You will have to read your manuals to find the exact syntax for the function.(If it exitsts.)

You might find it faster to return the record set "...where [field] like * &[search term] & *" and then itterate thru' the recordset doing an update little by little (unless the fields are more or less the same.

It will be slowish to VERY VERY slow to do it that way (depends on a bunch of stuff) so if Replace() works with your SQL version go for it. Otherwise welcome to slow-ville.