assign configuration package

There is a configuration file which is used to hold a connectionstring for the ssis packages.
Once the configuration file is created then is it necessary to go to each package and then package configuration to point the package to the configuration file?
It seems the packages do not automatically refer to the config file. Instead each time the config file is changed then all the packages have to be pointed to the config file one by one. i.e. going from Dev to live.
Am I right?
Thanks

Once a package points to a config file, you don't have to do anything when migrating to different environments, provided the package can find that file in the new environment.