Assumed you changed your 'app/controllers/application_controller.rb' and your deployment process works with capistrano, then you can execute the following steps:
1. Step (file upload)
cap deploy:upload FILES='app/controllers/application_controller.rb'
2. Step (restart of the application)
I think with this way it is really easy to avoid initializing a completely new release process. In some cases a completely new release maybe could be better, but in little projects, for example, it works very fine this way.