If I run
php app/console doctrine:schema:update --force
php app/console doctrine:schema:update --force --em="custom"
According to the command documentation, there is no such option. If this is something you have to do only once, I'd suggest to use the
--dump-sql option to get the required SQL instructions, and manually run the ones you need.
P.S. I fail to understand what's the reason to only update the schema for an entity, and leave all the rest of entities not sync'd with the database. That sounds like a recipe for getting db errors.