You can control the session parameter that defines the character set to be used for external representation from within the client application submitting the request. Specifying an alternate character set overrides the default client character set for a session.
For example, in BTEQ you can use the SESSION CHARSET command to set the character set for the current session:
.SET SESSION CHARSET 'ascii'
Make sure the character set you use (for example, 'ascii') exactly matches the name of a valid, enabled client character set.
For further information on how to use a session character set, see the users guide for the particular application.