It's a nebulous definition as far as I can tell. For what it's worth, I don't deal with these in any sort of legal capacity, but my day job does involve a lot of work with federal legislation and regulations--I'm just not entirely sure where legal terms might differ from my office's colloquial terms.
You can view the text of proposed and implemented regulations in the Federal Register:
https://www.federalregister.gov/
particularly under the Proposed Rules and Rules listings.
A rule will add to/amend/repeal some part of the Code of Federal Regulations. This can be anything from clarifying a few words or fixing drafting issues to implementing major regulatory changes.
It doesn't seem clear to me what this proposal would impact--does a minor amendment to an existing paragraph require a repeal of existing regulations? Would it need to meet some threshold of increasing regulatory burden--how would that be determined? What if it decreased burden?
You can look through daily issues and see that they tend to just be handling the daily business of the government. Today's includes changes to fishing zones (restoring access to an area that had been overfished a few years ago), adding more airworthiness checks to certain aircraft parts, reducing restrictions on certain tires for trailers, and adding restrictions against financial institutions processing transactions involving North Korea.
Would each of those need to repeal two prior regulations to take effect? What would quantify a previous regulation? And would they all be able to?