For a different use-case we have something similar to this internally that allows one to specify that set of keys to either keep or drop and perform a rollup on the rest with an aggregate function such as sum. I don't think it is needed for this PR, but I wonder if having JmxMonitorRegistry support an aggregated value of some kind would be a better option for dealing with collisions. The other benefit is it would allow one to control the tree depth in jmx.