Well, that's the expected procedure - when the updated definitions are released, simply let the new ISO be created and overwrite it over the CD-RW medium you use for BART.
You can supply the new definitions (VPS file) e.g. on a diskette, or if you have multiple CD drivers on the computer, maybe even on another CD - but I don't think it's very comfortable. The CD writers are quite fast today, so I think updating the whole CD-RW is simply the best.