Just tossing this out there, but from what I know of diesel truck emissions, and the way diesel engines and particulate filters operate, you guys might be taking this a little far...
Idling a tractor down when it's just sitting (once it's warm) shouldn't load the filter hardly at all. It's working the engine at lower RPM's that loads the filter. Most particulates are generated when the engine is lugging, or when it is trying to come up to the desired speed and adding significant fuel. Any steady state operation at low loading should produce much less soot loading, and that includes idling. Now, if you ONLY idle the tractor, it will take longer to warm up, and a cold engine does produce more soot.
My recommendation is to idle up to around 1500rpm's until the engine is warm, and don't work it until it is.
When working the tractor lightly, 1500-1800rpm should be sufficient. If you can hear it lugging, or see the engine speed drop while working it, you need to use higher RPM's.
Avoid constantly using the foot feed on gear tractors, as increasing engine speed while under load generates additional soot. Instead use the hand throttle like you would on a hydrostat. Set it high enough that the engine doesn't lug or bog as you operate the tractor.
As long as the engine is up to temp, and the tractor is not in a regen cycle, idling it down when it is just sitting should not significantly increase soot loading.
Of course you can just run it at rated speed all the time, but that's terribly inefficient unless you're working it hard all the time, and you'll rack up hours much faster than necessary...
Just my $0.02
On another topic, any of you running 31xx or 41xx series tractors care to comment on how often they regen? LS insisted it would be a LOT less often than the 30xx/40xx tractors, and I'm curious if they hit their goal... ???
