can sql update a non database ascii text file in IFS

I need to update text files received for import (not a database file) in
the IFS with only sql (the text files were generated weeks ago, cannot be
regenerated, and a two byte column needs to be updated before processing if
value = 99). I don't have an option to do an emergency release of program
code to fix it (at least not easily), but I can execute sql script with a
simple approval.
Is such a thing possible? It is many files (20 or so) and approx 100,000
rows per file.

psuedo code idea

update '/input/file1.txt'
set (substring,101,2) =
(select ordertype from OrdMaster om
where (substring,11,9) = om.OrderNbr)
where (substring,101,2) = '99'

and the order number in substring,11,9 is a character string matching
OrderNbr which is character.

TIA

Jim Franz