I am curious what others think about this, and whether it applies to more than just plants.
Per the International Code of Nomenclature (ICN) for algae, fungi, and plants (Art. 50 and Art. H.10.1 Note 1), changes like this are considered trivial nomenclaturally. Such changes (in either direction) do not involve a change in rank or authorship, nor do they require formal publication. Anyone can express an opinion that a published species name is or is not a hybrid simply by writing the name with or without the multiplication sign.
For that reason, I would suggest that there is no need to make taxon changes in iNaturalist for simple changes in hybrid status like this. It amounts to a “spelling change” for something that is already “spelled” correctly according to the ICN. Instead we can just add the hybrid or non-hybrid variants of the name to the scientific name synonyms to ensure the taxon can be found in iNat under either variant.
Of course this question becomes moot if curators ever get the ability suggested in this feature request: