You can specify a different default session calendar for a user by specifying the SET SESSION CALENDAR SQL text string as the startup string for the user by submitting a CREATE USER or MODIFY USER statement.
Assuming that the default business calendar for the site is Teradata, the following CREATE USER statement creates a user named john_smith and uses the STARTUP string for john_smith to set his session calendar to COMPATIBLE instead of Teradata each time he starts a new session.
CREATE USER john_smith AS PERM=10E6, PASSWORD=john_smith, SPOOL = 1200000, FALLBACK PROTECTION, STARTUP='SET SESSION CALENDAR=COMPATIBLE';