If you wanted the change to take effect then, yes, you would need to restart those apps. Because of the way that NixOS deals with dependencies, the old versions

If you wanted the change to take effect then, yes, you would need to restart those apps. Because of the way that NixOS deals with dependencies, the old versions would still be around for running apps to use and carry on. It might actually be a useful tool for NixOS: finding out which processes have a specific version of a module loaded, so that the user can be warned to restart those processes. If the user wants to restart processes they can, if they want to just reboot they can also. Simply because it's "simpler" to do one, doesn't mean it's the correct universal choice in all circumstances. My wife, for example, leaves way to much crap open and leaves her laptop suspended - a restart is a serious issue for her.