Double derabonons, called shvus dshvus, like asking a goy to do a derabonon, is mutar in most cases for a mitzvah.
Chas veshalom to say that all derabonons are mutar for mitzvos. They’re not. One can never be mechalel shabbos derabonon, not for mitzvos, not for loss of money, not for anything short of pikuach nefesh.