Then you might well have some Apache config files that have grown over the years into vast monstrosities of Alias and ProxyPass, then no-one understands what they all do.
So if you have a virtual host like so;
Alias /somethign /var/somewhere/else
ProxyPass /SomeMiniSite http://my.tomcat.server.local:8080/SomeMiniSite
You might find you want to split the logging for some sub-URI path like so;
/SomeMiniSite -> /var/log/httpd/someotherlogformat.log
One way to achieve that is via setting an environment variable based on the required sub-path like so, and using that to select the CustomLog directive
SetEnvIf Request_URI ^/SomeMiniSite SomeMiniSite
CustomLog logs/myminisite-access.log common env=SomeMiniSite
(you can switch the log format for the other CustomLog location
Apache supports piping the CustomLog like so;
CustomLog "| /usr/local/sbin/log_spltter" combined
Also there appear to be some virtual directives with the mass virtual hosting examples here;
with some ideas for log splitting based on a custom log format called vcommon
I've not consider what effect this would have on performance, so it would be worth keeping an eye on which is the most resource sucking.