Back in the earliest iterations of the ASF (“Amazon Seller Forums”), the term ‘cleaving,’ in the “forumese” of the old hands - who taught much to all of the rest of us that followed behind - did indeed typically refer to the first understanding you’ve mentioned.
However, in the first few years after the ill-fated TPTB decision to throw open the US Marketplace to direct sales from PRC-based sellers, Amazon realized that its former laxity in nice observance of Globally-acceptable GTIN standards had produced a situation that could cost significant diminishment of its bottom line, be it by regulatory action, or by market pressures upon its Sales Search Engine’s Big-Data number-crunching analyses, or by more-obscure possibilities.
As a result, Amazon introduced the afore-mentioned ASIN-cleaving process; by around mid-2015, the long-time vets began touting the ability of the Catalog & FEEDs Department’s Catalog Team to “re-map” Key Attributes like GTINs* - if, as Marbles mentions upthread, the appellant can indeed prove ownership of it.
It took some years longer for Amazon to even begin really cracking down on such spurious product identifiers polluting the catalog, as it did with the GS1 Initiative’s original deployment, but Cleaving Tutorials on how to achieve the moving of a GTIN from one ASIN to another were appearing even before then; our well-missed friends @Bad_Brittnie, @Roxy, @ShelfCleaningCapital, @Rushdie, and several others - including some active members of the SAS, as indicated in the above-linked thread - stand out with incisive posts they’ve all made on this topic over the years on how to get Amazon to sign off on doing this type of re-classification in its own best interests.
To be fair, we ourselves have not had to follow this route for some time, as we’ve only suffered a fairly-minimal impact from our own GTIN blocks being improperly assigned to an Amazon Global Catalog ASIN’s Offer-Listing which is spurious - but AFAIK, the avenue IS still available, as our friend @oneida_books’ alludes in that MoonDay55 thread linked above in Post #8.
*
Back in those halcyon days of one-to-one telecommunication with the cracker-jack experts of the Catalog Team being available upon demand (and when ya could get hand-typed notes/summaries in the associated case log without having to prompt for the rep to supply them, either verbally or ‘writtenly’), it was still not atypical for the rep being required to “engage another team” - one of Amazon’s euphemisms for the process of passing an exception request up the chain of command to a decision-making level, and awaiting for it to pass back down as approved, or not - but in that era, prior to the Help Hub Initiative’s deployment of predictive AI workflows, the waiting period was generally a full factor of magnitude shorter (i.e., 3 days, or less, rather then the currently-more typical 30 days or more for so many case types).