yes easily done, you just have to go around the scrap yards or search ebay for a hlx thats breaking. as for the heated seats best just fitting them yourself-
Chances are the relay is already in place. All you'll likely to need will be the wiring loom for the bumper itself (plus obviously the bumper and lights). Oh and the switch for centre console.
My 1.2 is now HLX spec with the exception of the engine now
So yes its certainly possible.
Longest Serving BOO Member
Bravo: Nov 01 80SX / 75,000 miles
Coupe: Feb 97 20V N/A / 135,000 miles