Unlikely that Edit > Replace would work since you probably have 1,800
different replacement product numbers for the original set.
But a simple vlookup might suffice though.
Here's an example:
Assume the original-new product number reference table is in a sheet: x
in cols A and B, data from row2 down, eg:
Orig# New#
11111 PK001
11112 PK002
11113 PK003
etc
Assume your orig product source data is in Sheet1,
data running in B2 down, eg:
Orig#
11112
11112
11113
11111
11113
etc
Insert a new col C
Put in C2: =IF(B2="","",VLOOKUP(B2,x!A:B,2,0))
Copy C2 down as far as required. Col C will return the new product numbers.
If desired, kill the formulas in col C with an "in-place" copy n paste
special as values, then clean up by deleting col B.
---