What would it take to reclassify a schedule 1 substance as something else?

No beating around the bush: This is about cannabis.

United States Code § 1703 (b)(12) (a federal law) requires the drug czar to “take such actions as necessary to oppose any attempt to legalize the use of a [Schedule I] substance.”

So by law, the drug czar (currently Gil Kerlikowske) isn’t allowed to even consider decriminalization or legalization. What can a citizen do to reclassify a plant as a non-schedule I substance?