The information is taken from public documentation supplied via Apple. Changing the APN on an iPhone is not a hack of any kind. It is done the same way as Apple supplied software does it, but with a nicer and easier method than Apple's tools.
The FakeAPN sets the APN to a random value. As (most) phone carriers need a valid APN set on your phone for it to access data, setting it to a random value should make it fail in connecting (so your data is disabled on the phone). There are some carriers who just ignore that you put in the APN Settings and will just work so setting the APN to an invalid entry won't stop data. Usually there is an APN you can set specificlly which will block data in these cases.
Also coming on in newer versions of software for the iPhone you will have the option of turning off Data with an option on the iPhone.
Apple does not give any way of settings MMS Settings so they cannot be sent in an automated way. On the iPhone 4S you can do a SIM Swap Method as described HERE to enter MMS Settings
You will have to add a Data Feature to your account for Data to work properly. The $50 "unlimited" plan is not unlimited on Smart phones and you have to add a Data Feature for Data to work.
I am 100% it won't. It doesn't jailbeak/hack or otherwise your iPhone and uses the same method that Apple's supported software does it as well.
Some iPhones by default, the APN Settings are hiden so you cannot change them. This decision is made by the the original Carrier the iPhone was sold via.
Most of the common APN Settings for various countries are listed, but if you can not find one which works then please contact me with the Country and phone carrier you are with.
You will need a wireless connection to gain access to the internet via your iPhone @ first to install the APN Setting. These days there are alot of public access points available freely to be used such as places like libraries etc.
Your iPhone has to accept the non official sim card in the first place. There are quite a number of countries who sell carrier unlocked iPhones (or allow you to pay them to be unlocked via the official carriers).
If you think a question should be on the FAQ please contact me.