It looks tricky but its really quite straight forward ( says I after following the guides on here
Definitely remove the seat, its easy and makes the job a lot easier.
I did both of mine a couple of months back, 1st one took me over an hour, 2nd one about half that.
The guide on here was great but as above some stages can be omitted, I didn't remove any upholstery staples, I taped the new cable to the old and used it as a draw wire.
Remember to use some grease on the mechanisms once you've got access to them.
Another good tip I got on the forum was to push the seat back ever so slightly when pulling the handle to get access in to back seats, takes the pressure off the mechanism and handle.
I take it it's definitely the cable that's snapped and not the handle itself, if the cable still has the nipple on it then I think
you can just replace the handle part in situ