There are a lot of topics on the forum that address the creation of common names. You may find helpful info in:
https://forum.inaturalist.org/t/common-names-invented-on-inat/27452
https://forum.inaturalist.org/t/the-right-of-a-fly-to-a-common-name/14842
https://forum.inaturalist.org/t/common-names-from-not-good-enough-sources/14976
https://forum.inaturalist.org/t/just-how-does-one-coin-a-common-name/27506
https://forum.inaturalist.org/t/reliable-sources-for-common-names-on-inaturalist/5579
The shortest answer is that iNaturalist does not allow the creation of entirely novel names on iNat itself (though some users may do this anyways…), but does allow adding those that have been used in other sources (though the exact nature of what those sources are/should be often receives debate as evidenced in those threads).
One of the primary reasons for adding common names is to facilitate users finding species using terms and names that may be familiar to them (when they may not know scientific names). In the case that you outlined, it doesn’t sound like the name is currently in wide usage for this species, so it won’t fulfill this goal. @earthknight has also given several good reasons against using this common name as well: that this common name is a general descriptor of a variety of species and already commonly used for another species. Given this, it seems like adding this common name for E. atrata might cause more confusion than clarity, and should probably be discouraged.