I have a string of text ("AAA1000project1", "AAA1001project2", etc.) that is used as an identifier for projects. This field is a text field. I need to write a script that checks the triple letters and the number but drops the rest of the text in the field and compares the new entry (which is done manually) to the existing records so that the number is not duplicated. I do not want to create more fields and break this one field up, unless there is no other way to do so.

If you create one extra calculation text field equal to Left( field, Position( field, "project", 1, 1 ) - 1 ) and a self-relationship from this field to itself, then your script can Exit Record/Request and test If [ Count( selfrel::id ) > 1 ], in which case there are duplicates.