Я так понял, что всё же мне не имя сервиса требуется, а имя пользователя. Или есть какие-то неочевидные нюансы?

VARIABLE SUBSTITUTIONS

Many of the strings that are settable in the config file can take substitutions. For example the option “path = /tmp/%u” is interpreted as “path = /tmp/john” if the user connected with the username john.

This allows you to include one config file inside another. The file is included literally, as though typed in place.

It takes the standard substitutions, except %u, %P and %S.

The parameter include = registry has a special meaning: It does not include a file named registry from the current working directory, but instead reads the global configuration options from the registry. See the section on registry-based configuration for details. Note that this option automatically activates registry shares.

Default: include =

Example: include = /usr/local/samba/lib/admin_smb.conf