To allow for more customization of the exim.conf, more .include_if_exists statements should be added.
In this particular case, I would like to have a way to include an additional file for each of the already defined transports. This is needed to configure shadow_transport as described in forum.directadmin.com/threads/backup-all-incoming-mail-using-shadow_transport-in-exim.63381/.
It would make sense I think, to include a file named after the transport name itself, similar to the one already present for the 'virtual_localdelivery' transport.
Here's a diff that would add such lines to all my current transports. The filenames should maybe have 'transport' in their name, to avoid any possible collision in the future.