I have done this back when we upgraded from LabVIEW 4 to LabVIEW 5x. The problem lies in the fact that the TE source is under tight control; in LabVIEW 4, you could remove diagrams to prevent user access. LabVIEW 5 did not allow saving distributions without diagrams, so the source is password protected (and I do not have the password! It is under tight control by NI).
To upgrade the version of TE to add back-panels, refer to
this National Instruments Knowledgebase Entry, titled "LabVIEW Test Executive 4.0 for LabVIEW 5.0" (Document ID: 17QDPKPL). Here is the associated
ftp link (as the Document ID has changed from when I first ran into this problem).
I've used the above method to upgrade from TE4.0 on LV4.0 to LV5.1, while encountering very few issues in the upgrade.