Ok, but you're still not explaining how that works in the actions side of things.
In order to compare two different instances in the same action there has to be an expression that picks the instance and uses its value.
What I described with the object index is virtually the same thing, except it does not work within the confines of the collision, other than in the condition pick nth.
If it is possible, that would be the cleanest way imo.
Also named strings are a fuzzy subject, as there are security, and minification concerns.