Last time I did a Clojure project, we've constrained the hell out of such maps with Clojure's Spec feature.

Despite spending my last few years working with Common Lisp and a bit of Clojure, I've grown fond again of type constraints. Typing your data prevents a lot of silly and easy-to-make mistakes. Spec in Clojure is doubly useful, because specs can serve both as tests and generators. So after you define how your data is supposed to look like, you can make Clojure start pumping out randomly-generated examples, which you can then use to test your code.

(Note that typing maps with Spec doesn't mean they're inflexible, a priori structures. You just pin down what you know. In this case, you could define that a "person" needs a :name key, and can optionally have :admin?, :mod? and :nickname fields. If it also has some other fields, no harm done.)