Is it possible for the laymen to change the sensors near the engine block. Will this require special knowledge or extensive work to achieve ?
I don’t know about the Crown Vic, but on most cars it is relatively simple to change out the O2 sensors, but you need tp purchase or rent the special O2 sensor removing tool.
Accessibility is the issue here. You can see the sensors. And by that I mean that you can see them and think “How the heck am I gonna get my arms in there?” There’s nothing technically challenging if you have simple oxygen sensor socket, or just cut the wires off the old one and use a 7/8" deep socket. No special knowledge or training needed.