I did this on ours a couple of years ago and it's not too bad.
A few years before, our cat had been cut out and stolen, so I bought a complete exhaust including cat for about £220 from eBay and fitted it. The cat section was good, but the fit of the rest of the exhaust wasn't right, and it always hung lower than it should which meant it scraped over speed bumps.
I decided to change the exhaust from the cat backwards, and really it's all about getting the 3 nuts undone on the triangular flange where it joins the cat.
If those come off, then a big screwdriver and a can of WD40 are a great help pulling the hanger rods out of the rubber hanger mounts.
I looked around and concluded that Klarna seemed to be one of the better manufacturers and managed to get one online for about £100 for everything backwards from the flange.
Be aware that modern exhausts seem to rot very easily wherever they have welded hanger rods or flanges, so it's well worth wire brushing all those rusty areas and spraying them with a decent exhaust temperature rated paint before fitting as it will probably extend the life by a couple of years perhaps.
You might find that the bolts that hold the rear box to the centre section are tough to get undone, but persevere with heat and spray because I think they're about £14 each and they are available from Febest if you just can't get them out.
A new flat triangular gasket is a must, but I ended up making one from thin copper sheet with a smear of gasket cement and it's been fine.
A good high lift trolley jack is a big help, and an impact gun or heating torch is also useful.
Consider replacing the 3 nuts at the front flange with non ferrous ones as they don't rust firmly in place.
