I have fiddled a lot with Eagle seats and here is my advice. Getting the seat out is pretty easy. Each seat has four nuts that you access under the car. A couple of them are a little hard to get at. Rock the seat to get it out because it may be fused to the carpet with rust.
Putting a seat cover over an existing seat will work, but will never give you a custom job. The original seat cover is held on by loops of cloth at various locations of the seat and anchors that tie to the seat frame and spirngs under the seat with hogrings (steel circular tiedowns). The seat has to come out to remove these and detach the seat cover. Once the seat is removed from the car, p[ut the seat back in the farthest down position. Detach the seat adjustment handle and plastic cover at the pivot point for the seat back. Remove the screws that appear under this with a torx wrench. Take a screwdriver and pry the plate outwards and work the seat back off. Turn the seatbottom upsidedown and remove hogrings and work the seat cover off. Generally, you will find broken springs on the driver's seat.
For the back, you need to remove the headrest. For this, you need to slip a thin piece of metal down the down the support bar into the seat to release the catch.
Often, repairing a panel of a seat is difficult because the old vinyl becomes stiff and tends to break when worked with. The seats covers I have had redone were taken apart and the pieces used as patterns to make a new seat cover. The cost in the States is a lot because this is very slow work. My wife is Filipina and we just returned from a trip to the Philippines. I took along a pair SX-4 seat bottoms and had all the vinyl replaced and used the existing center fabric. I paid about $47 for the two.
Seats from an SX-4/Kamback and other Eagle models are interchangeable. I have done it. However, putting seats from another car in an Eagle will take a lot of fitting to make them fit right. I think I would stay with Eagle seats unless you aren't fussy and just want a daily driver.
Also, concerning the hog rings, you can buy the rings and the tool to install them at car parts stores or from JC Whitney. I have used regular plastic slip tiedowns as well because they are easier to install.