Len,
Not at all, a correctly designed engine management fuel/ignition map, SHOULD be more efficent (To a point) and therefore have LESS emmissions, never had one of our conversion fail a test on fueling at all.
50bhp is a decent hike in performance, along with the proportinal increase of Torque (more important on a road car) too.
Use a serial port type aftermarket upgrade, you car 'purchase' them for an hour and if you like it, they'll reprogramme th ecu according (up to 7 stages), and when the wagon goes back for services, you just remove the said upgrade with a key the provide, re installing it after the service. simple and effective. Wm