Just to let you know that this is some what possible in the current launcher using the edit mod pack functions you are free to add any mod you like to the ftb modpack for personal use, this would not be creating a mod pack but more like editing an existing one to you liking. please bear in mind that the magic worlds pack and the ftb pack are 2 separate mine craft versions ( 1.4.5 and 1.4.2 respectively).