Can you change the commerciality of a supply or service once it has been determined to be a commercial supply or service for a follow on contract? Where is that rule reflected?
Absolutely. It's up to the current contracting officer to make the commerciality determination. DoD's Commercial Item Handbook
states: "Contracting officers must ensure that contract files fully and adequately document the market research and rationale supporting a conclusion that the commercial item definition of FAR 2.101
has been satisfied." (p. 3). While precedent matters, new information or insight by the current contracting officer can change the determination for the follow-on contract.