Unless I am remembering very incorrectly (and I may be), the way that CA validates idno is through app.conf's "Require input id number value to conform to format? (0=no, 1=yes)" and if yes, then through multipart_id_numbering.conf.
Right now, in Itinera, the system has no problem with our idnos for, say, objects (they look like this WKYYMMDD##_inits) or any other major entity.
/data/web/itinera/admin/app/conf/app.conf currently is set to "no" on line 151, so CA shouldn't even be checking for validation, I don't think.
See attached for the error we get when we try to enter an idno for a tour stop.