FYI, the delete one UDM at a time model was implemented by design. (I didn't want the user to be able to delete all UDMs accidentally.)
However, you could do it using a third party tool outside of JCapper.
For example:
The data for all of your UDM Definitions is contained in the Profile and Profile2 tables inside of the c:\2004\JCapper.mdb file.
The file extension (.mdb) means that the file itself (c:\2004\JCapper.mdb) is an Access database file.
If you were to open the file (c:\2004\JCapper.mdb) using Access, you would then be able to open the Profile table - exposing the UDM Definitions in a data grid.
From there, you could highlight multiple UDMs in the data grid - and delete all highlighted UDMs with a single press of the delete key.
And from there, using a similar procedure - open the Profile2 table - and highlight and then delete the same UDM names.