SUMMARY The phrase "invoke action" is vague and technical, and I actually still have trouble figuring out what it actually does. Often it does nothing (https://bugs.kde.org/show_bug.cgi?id=440727) but I get paranoid that it did something unspecified invisibly or think it's broken as if something unspecified should've happened, because I don't know what the "action" is supposed to be. It'd be great if the text changed to say what it'll actually do for an entry -- "Open webpage in...", "View image in...", etc. Would be even more great if the generic (window with a play button) icon could be context-aware too.
I'm not sure how feasible the proposed solution is, since the menu text would need to read user-defined arbitrary rules and use their descriptions to determine how to change the menu text. And then what happens if more than one configured action matches? There may be other possible solutions to the core problem of not having any indication of whether a rule was triggered. Perhaps something can be popped up when a rule is triggered, with its description. I'll let the developers weigh in on this. In the meantime, you can always review the configured rules in the clipboard settings to understand what rules you've configured and how they would affect text.