http://www.doorfurnituredirect.co.uk/scpro/bernards/productscategory~p arentcat~54~parentcatname~Draught Proofing and Thresholds~prodca t~413~prodcatname~Weather Trims and Thresholds~page~1.htm

The lead isn't that much of an issue if you don't release it in chips or small particles. Could you just use a small plane to shave off a thin layer of painted wood and bag and dispose of it? I also think just popping the threshold and replacing it is as easy as looking for adequately sized exterior metal covers.

As an alternative you could use one of the Peel-Away type paint removers and get rid of the paint in a couple (at most) coats. Then repaint with non-lead paint and you'd be good to go. The peel-away products can be expensive to use for large projects but for what you're talking about it shouldn't too bad. And because they encapsulate the paint (when you peel it away) there is less chance of chips breaking off and getting ground up into dust.

Almost any gel-type (even if not peel-away style) of paint remover, if used carefully would work. A fairly un-stinky, but still effective, one is made of soybeans (Soy-Gel?). I've used it on floor paint and it melts the stuff enough for efficient scraping, with very little problem with bits falling away. Then you clean the wood with a citrus stripper. Since your're going to repaint, I would simply go over it with fine steel wool, then repaint. No need to sand, unless you want a super smooth surface which would be somewhat wasted for a door threshold, anyway.

HTH,

Molly