Yes, with CA Easytrieve for Windows, you can append data by using "SEQUENTIAL CREATE" at the FILE definition.
When using "SEQUENTIAL CREATE RESET" data won't be appended.
Here is a small sample - the "append1.pco" program was executed on 08:40:52 and 11 seconds later again à
<Please see attached file for image>
Release: EDBMSU00200-11.6-Easytrieve-Report Generator-Option for DB2-MSU