It would be nice to support this. To do it you'd have to read all the children (to cache their data), then add steps to remove all of them, then add steps to add them all back.

Hmm, maybe that's not even necessary. As long as the new value includes all the existing values (i.e. it's not doing an add or remove) it could just be stored. A reload would be required though.

Anyway, this isn't something to hold up merging this.