Free translation of Haqdamah:
And if in some lands they have a minhag to prohibit some things,
even though that we decide the opposite,
they should remain steadfast in their Minhag
because it has already accepted the Hacham who prohibited,
and it is prohibited for them to have a minhag permitting
as is found in the Fourth Chapter of Talmud Pesachim.
Question: Whose Haqdamah contains this disclaimer?
Surprise answer: The Beth Yosef!