nginx: how to overwrite one directive

I'm trying to organize my vhost configs in several files, so that there is a view basic files / "templates" and the rest just include them and overwite settings as needed. Here is described, how the inheritance in nginx works. What I'd like to know, is: (how) is it possible to overwtire not the whole setting block / context (e.g. server), but just an option (e.g. server_name).

Example:

I've defined a server block

server {
    listen   80;
    # server_name is not defined

    if ($host ~ ^(?<project>.+)\.(?<area>.+)\.loc$) {
        set $folder "$area/$project";
    }
    ...
}

and want to set/rewrite set the setting server_name in another place. It should be look like

server.server_name foo.bar.loc;

Dotted syntax is not allowed. But maybe there is something like this?