In order to customize the AS/400 sign-on display, you must first create the DDS that you want to use for your sign-on display. There are 2 ways to accomplish this: modifying IBM's sign-on display, using member QDSIGNON in the physical file QGPL/QDDSSRC; or by writing your own DDS and copying the fields in QDSIGNON.
In either instance, all IBM fields must remain in the same order in the display file, but you can reposition them on the display. The only IBM field that can be modified is the UBUFFER field, which is the last field. The 128-byte field can be modified with input/output fields thus allowing users to input data into the sign-on displays.
The UBUFFER fields can appear anywhere on the display, but they must follow the IBM fields in the display file.
Compile the display file. Once the display is created, be sure to test the new sign-on display on one subsystem or on a test version of a controlling subsystem. By issuing the CHGSBSD (Change Subsystem Description) command, and specifying the new display file on the SGNDSPF parameter,
the subsystem will now use the new sign-on display. Once testing is complete, you can change the subsystem descriptions for all the subsystems for which you want to use the modified sign-on display.
For example, for subsystem QINTER, issue the command CHGBSD QINTER SGNDSPF(your library/your file)