Editing a message catalog definition in PeopleSoft is pretty straight forward, simply browse to the following menu path:
Enter your message set number into the prompt. Note that if you do not know your message set number you can use the following to find it:
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SELECT * FROM PSMSGCATDEFN WHERE MESSAGE_SET_NBR = '12345' AND MESSAGE_NBR = '12345'; SELECT * FROM PSMSGCATDEFN WHERE MESSAGE_TEXT LIKE '%what your message is%';
Once you have your message simply edit the text and description appropriately then save!