Air Conditioning - Must I buy a special AC unit? (thru the wall replacement)

Every AC unit in my house is thru the wall. Enough of them have died or have problems so it's time to start upgrading. Sliding the 'guts' out is easy - i've traded out a broken for a non broken unit- but on a new AC unit, do I just take off the cover and (assuming it's the same dimensions) and plug in and go?

or do you have to buy special 'thru the wall' units that are made to have their covers taken off?

There's no way I can go thru the hassle of taking out the old cases. They are 'in there' pretty good and I'm not messing with the outside permastone and all the things that would happens should I decide to remove each shell.

I do realize I can just put units in the windows, but I hate losing a window that way. Plus the one unit is 7 ft up on the wall in the living room and is nice and out of the way.

Shop around mark down how hig and wide they are what size. There are all kinds of AC like that that slid out of the case. like yours do.

ED ;)