Creating new variables in /etc/apache2/envvars?

This is not directly replying to the question but according to passenger documentation, production is the default environment so you shouldn't be needing this line. (I'm guessing you are using passenger)

Edit: I've tried putting PassEnv APACHE_RUN_NEWVAR in my vhost config file and it worked. It wasn't working before.

See the doc :

Specifies one or more native system environment variables to make available as internal environment variables

Edit2: Seems like PassEnv has nothing to do with it. When I reload the config with apache2ctl restart the new variables are not defined but if I do apache2ctl stop then apache2ctl start it works fine...