Postgresql 9.6 restriction

Hi,

I want to upgrade my database from postgresql 9.2.15 to 9.6, we have username start with pg_abc_c as sysadmin user, all our installation owned by pg_ users. Now issue is with postgresql 9.6 onwards, you can't create role/user with pg_* when initialize system.

* Treat role names beginning with pg_ as reserved (Stephen Frost)

* User creation of such role names is now disallowed. This prevents conflicts with built-in roles created by initdb.

What are options for me? We use pam authentication. I tried using pg_ident.conf to map users, but it does not work with our authentication method.
authentication option "map" is only valid for authentication methods ident, peer, gssapi, sspi, and cert

Please help.

Thanks,
Yogi