Yes,
255/35/18s and 225/40/18s will have a similar overall rolling circumference and diameter.
the profile (35 or 40) isnt in millimeters, its a portion of the width of the tyre i think.
a 235/40/18 will be very slightly larger actual profile than a 255/35 so itll pick the back end up by a couple of millimeters.
oh the extra width on the back will help traction a lot, and I think that 255s on the front would be bad for steering, 225 is easily wide enough I would say