Whereas in a nomenclatural sense Marmosa regina Thompson 1898 was recently revealed to be a synonym of M. isthmica Goldman 1912,* in a taxonomic sense—iNat's sense—M. regina has been essentially universally used (including by the IUCN, iNat's former mammal taxonomic authority, i.e. the source behind the former M. regina concept, range map, etc. on iNat) for varying taxonomic concepts in the subgenus Microureus; see Giarla & Voss 2020 for details. The IUCN concept of M. regina corresponds (I think) to four species currently recognized by MDD (and thus iNat): M. germana, M. parda, M. rapposa, and M. rutteri (following Voss et al. 2020 and Voss & Giarla 2021). Accordingly, rather than being swapped to M. isthmica (resulting in an erroneous range map and some misidentified observations), M. regina should've been split into those four species (perhaps alongside a couple more formerly treated as conspecific). (Marmosa isthmica, in contrast, should've been split from M. robinsoni along with M. simonsi; M. robinsoni still includes isthmica and simonsi as subspecies.) I'll create a couple splits to resolve this (and fix the range maps as well).

* while M. regina is a senior synonym of M. isthmica and thus has priority, a case has been submitted to the ICZN to suppress the former name, due to the confusion that would result from the transfer of the name from the taxonomic concept that it was long used for to an entirely different taxon that has likewise long been known by a different name; for the time being, the junior synonym M. isthmica is to be retained, per ICZN Article 23.9.3