You can nest functions:

REPLACE(REPLACE({saleunit}, 'Each','EA'),'Carton','CT')

There may be a more clever solution! If you find that you need to do this translation frequently or in very different contexts, please consider a custom read-only field that automatically translates the unit to the display value. That way, you could simply refer to the custom field, whether the context be search, report, template, script, etc.