I changed my s1 to a neo and nistune, step 1 change to manual saves about 1/2 off the loom transfer, but still it's a bitch of a job loom has to be spliced to operate between s1 and s2 , as aircon, abs, altessa all have inputs and out puts running through Ecu , so it's quite a big wiring job even with out the auto and if you had to pay an elecy who knows what he is doing would charge over 1k ,
If your only reason for doing this is fuel economy don't bother, not going to make that much diffrence , . If not piggy back an emu or the likes to a s1, the only reason I changed to neo was it was the start for some moderate decent power, with a stronger engine and it was a step to where I heading now/next with my build I also wanted to run and tune with nistune much more economically viable for me . You can just put a neo engine in swap the cas wires around and it will work but you will still have to piggy back onto original Ecu.this way you can still leave manual. I used and tuned my old e manage ultimate on my old auto s1 set up made 240kw on pump98 with an auto fuel pig though .