The front bumper cover comes off with a few torx in each wheel well, a few under the center upper grill, and a few behind the lower grills. If you have a skid plate or belly pan, make sure any torx between the two are removed. I'd say it's 20 min not counting any prep. The headlight assembly goes in the oven at low temp for a few minutes, remove the old lens, and replace. If the old lens is OE, and carefully removed, the butyl rubber sealant is usually still good, and while warm will nicely receive the new lens. The OE type of buytl rubber sealant is available in a roll from Amazon for cheap.I bought some as a "just in case," but I think I've only used a section once. I've not yet had a problem with a new lens flaking or clouding, the primary concern is usually that the aftermarket polycarb is more brittle, doesn't fit right, or doesn't have the same optical clarity. These haven't been an issue with even the cheap one I've gotten from ebay. The OE headlight housings aren't designed for HID bulbs, and I haven't yet seen LEDs that are cost effective compared to a good H7 (of course, that's for the Golf, and the Jetta headlights are notably less effective). More posts available on this through a search.
The methods above are all helpful, and obviously each owner finds a method they prefer. In terms of time and effort, if we put two MkIVs side by side and made a full effort to properly polish and seal on one, and replace lenses on the other, I'll bet the lens replacement is quicker for those who have removed the bumper cover before. That effort results in a decade-long solution. No knock against the above products and techniques, but I haven't found any that last very long (24 months at best, but often 6 months before there is a decline). Heck, take a can of clear lacquer to the salvage yard and with no other effort, just spray an old MkIV headlight- it will look quite nice....but it won't last.
Take pics for us after you decide!