Rooting and unrooting Apex Launcher I read the ApexLauncher FAQ and there is this line:

Move the APK file to the /system/app directory manually. 
Make sure you set the file permission properly. 
Please reboot your device if the in-drawer widgets feature does not work. 
To uninstall, please remove ApexLauncher.apk from /system/app manually.


My question is, is it really that easy to do? I mean, if I move the .apk to the system directory, I will have a fully-functional ApexLauncher (i.e. a rooted phone) and when I delete the file, I will be back to the OK-state?
No. To move the app to /system/app directory your phone must be already rooted. You would want to install Apex Launcher as system app i.e. install in /system/app because of the following reason.


  NOTE: Due to limitations of the Android framework, you won't be able to add widgets from the drawer unless Apex Launcher is installed as a system app (root required). Please read the FAQ for more information.


If I misunderstood your question and if you were asking if installing app as system app in a rooted phone is that easy, then the answer is yes. You can do it as you have said and once you remove it, your phone will be back to the "OK" state. You can also use program like ES File explorer or use adb to install as a system app.