Note that VACUUM FULL and CLUSTER can update ctids. I don't believe regular VACUUM can, so you should be safe from autovacuum interfering in this scheme, but the ctid colum documentation [1] states "A primary key should be used to identify logical rows," so this is not exactly intended usage.
Thanks, Maciek [1]: https://www.postgresql.org/docs/current/ddl-system-columns.html
