I purchased a $50 Dremel from Home Depot & bought a smaller bit with saw-like teeth. The fact that it was smaller was better for me becuz it reduced the chance for error. I took apomerans advice on the cutting technique. He posted it on blackedout5's post about his headlight job. I cut behind the lip everywhere except where it was impossible due to the design of the housing. On those points, I cut on top of the lip. Once the cut was complete, I began to break the lip away with a flathead screwdriver. Easy to break but won't just come off due to the rubbery BMW seal. Just peel it.
After the edge of the plastic lens is mostly visible, I go @ the seal with a box cutter. Couple inches @ a time, just running the blade through until its relatively snag free. @ some points, your gonna have to insert a flat tool and gently pry up on the lens to stick a blade in there to cut the seal. After a while, parts of the lens will show signs of detaching. Focus on those parts & cut from there. Before you know it, the lens will be off. That's the most difficult part. How you clean & what you clean the lens with is your preference. Compounds, headlights restoration kits and the like. I sealed them back with a generous amount of black gasket seal on the point of detachment. Taped them up, let them cure, then put them back in.
One thing to look out for is ... you'll probably have to unscrew the ballast or whatever that is on the bottom of the housing to make a proper cut. Be careful of how you put it back in and make sure that the connections are free of debris from the job. Also, be careful of the reflector on the inside of the headlamps. I thought it would be wise to make sure that the interior was flawless before reattaching the lens. Went to hit it with Windex ... Yikes. Luckily, before doing any real damage, I noticed the mirror like paint was rubbing off. Please don't make that same mistake. Other than that, it's pretty straightforward. Good luck guys!!