Not too tricky, though it'll be easier if you can get the rear of the car up on ramps or axle stands.
Most towbars these days come with captive fixings that mean you don't have to drop the bumper. You just pop them through the slots, twist them to lock into place and then bolt the towbar into them. If your bar comes with standard nuts and bolts to fit the rear cross-member, then the bumper has to come off. Though that's not such a big deal either. The only snag that I hit was that I had to scrape off some of the underseal to get the bar mountings to go into place.
There will also be arms to connect to the chassis rails further forward. If I recall correctly, these should also come with an insert to shove through the chassis rail so that you don't crush it when you tighten the bolts. The left hand one is a bit of a pig to do because of the exhaust shield (don't do this job with a hot exhaust!)
Electrics are a different kettle of fish, though if you've done a towbar before, they shouldn't really be a problem. I wouldn't bother with bypass relays on the Lag 1, though some might disagree with that viewpoint.
Be sure to torque all bolts to the values specified in the installation guide, and the job should be a good 'un :d