At Omnigres [1] we also use libpg_query for programmatic query manipulations as libpg_query has a deparser and that allows one to manipulate AST and output the text representation back.
I'm trying to find time to contribute Postgres 16 support to it!
[1] Omnigres: https://github.com/omnigres/omnigres
We at pganalyze have plans to add Postgres 16 support to libpg_query sometime between the RC1 and the final release - mostly to watch out for the rare case where a feature gets reverted during the beta releases.
If you'd like to have a go at it before then definitely welcome (here is some context on the extraction process using libclang: https://pganalyze.com/blog/pg-query-2-0-postgres-query-parse...), and we'll also need people to test the PR once available.