Hi Frank!
That is a GREAT question!
Yes, Changeovers are collectible. In the Charlton Catalog it explains what changeovers are and also give pricing for them.
A Changeover is a point where there is a change (Either a Signature Change, Year Change, Paper type Change ect...)
Sometimes it can happen Mid-Prefix. A Perfect example is with the 2002 and 2006 $5 Notes. The last prefix used by BAI (Formerly BABN) for their $5 notes was AOF. They printed up to the serial number 3799999 in the 2002 (Non Security Stripe) $5 Notes. So it was also a Short-Run prefix.
Then in 2006 when the new $5 note debut they started with serial number AOF 3800000 and went up from there. So our changeover point was 3.800 million. This is also a very special changeover as it was a year change AND a note change (Upgraded Security Features).
Changeover's and short run-prefixes always carry a premium, some more then others. A good example of a higher premium changeover is the 2002 $5 HOH prefix. There was a year changeover from 2004 to 2005 mid-prefix as well.