How to rename a nested JSON field?

How am I supposed to rename a nested json field? Suppose I have input like

[{"Body": {"meta": ... }}, {{"Body": {"meta": ... }}]

and I would rename "meta" to "renamed_meta"

What works is:

mlr -j rename Body,renamed_Body <file.json>

This renames Body to renamed_Body

but this failes:

mlr -j rename Body.meta,Body.renamed_meta <file.json>

How am I supposed to rename a nested json field?