Time and time again, the SRM transition from GridFTP to HTTP creates problems. One proposed solution was to have the client overwrite the global TURL_3RD_PARTY_PROTOCOLS setting by passing 3rd_turl=<protocol_list> in the opaque info. However, while this solution would work for Rucio, we've faced the same transition problem on FTS3-Public, where not all communities are expected to submit via Rucio.
The FTS team will take control of this by making the TURL_3RD_PARTY_PROTOCOLS configurable per link. FTS will read the values from the link table (t_link_config) and pass them to the fts_url_copy process, which in turn will load them into the Gfal2 context.
Final note: This setting will not be exposed via the REST Server config interface.