There are generally two types of removable crimp terminals used in Ford wiring harnesses:

(1) Spade terminals with clips; the access is on the front. You must hold the crimp terminal in place in the housing from the back, while pushing the clip down from the front. The wire then slides out. You'll have to bend it back in place before reinstalling.

(2) Block spade terminals, which are larger. They are held in place by a tab in the pigtail itself. These are removed by bending the plastic tab from the back, and sliding the wire out. These are much easier to deal with.

It has been a while, so I can't remember which. If each connector has a small keyway on the front of the pigtail above the center of where the spade terminal from the switch would insert, it's the first type. If not, it's the second type.

In either case, you have to disconnect the switch first; you cannot remove the individual wires with the switch connected. You do not have to remove the individual connectors first to remove the switch, otherwise it would be a chicken and egg problem. If all you need to do is replace the ignition switch, you don't need to worry about the pigtail itself unless it's burnt or damaged in some way. Access is tight, but the pigtail does not need to be disassembled. I have not seen the pigtail sold for 78 models.