There are a few mitzvot which are effected through the use of that which is specifically forbidden. The first two examples are of tzitzit being made from shatnez and the mei sotah being infused with the ink from erasing the shem hashem. In an associated sense, we are mikayem the mitzvah of matzah through the use of a flour/water mixture which would be otherwise forbidden on pesach (though it is not precisely parallel). An even further extension might be that a kohen gadol or a nazir can be metameh himself for a met mitzvah (Mishna Nazir 7:1, "A Kohen Gadol and a nazir do not render themselves ritually impure for their relatives, but they may become impure for a "met mitzva"") And as a logical end, we have that pikuach nefesh pushes off everything and safek nefashos pushes off shabbos. But I am looking more at the specific mitzvot which override specific laws, not just ones which allow us to push off 'all' that is forbidden.
Are there other specific mizvot which are fulfilled through an action or a thing which would otherwise be forbidden?