paddysaab,
You can fiddle things through without taking the seats out. Though I've done this job a few times I can't remember all the details. To me that means it was fairly obvious and straightforward. One thing I do remember is to attach a piece of stout wire to the end of the old cable at the handbrake end. Use the old cable to pull it through then use the wire to pull the new one in. This gets around all the monkeying about trying to get the cable above the tank. I've known people drop the tank to get it back in.
Paul @ Kippen.