What do the .412's measure? Mic or measure with a good set of dial calipers to see if they are indeed, .412.

They may be .4115" and if so, or even at .412, if a new bullet fits easily into a fired case mouth, the .412's will work just fine.

Lee can make you a die as noted by 50Calshtr, however they may not list the die you want on the web site - you would have to phone and speak to the Custom Department.

We here at NE have been sizing down oversized bullets for years.

The .001" may work just fine as noted above. Start at the first suggested load in a manual and go from there. Don't reduce manual loads below their starting place.

.001" oversize is generally no problem at all, as long as the rifle's chamber neck isn't too tight for them. To have a problem with a mere .001" is highly unlikely, afterall, it is only .0005" per side.