Tearing Q'RIAH during Chol Hamoed
Beer Hagolah 8
Ba'er Hetev 4
Shaarei T'shuvah 4
Mishnah Brurah 16,17
Restricts Q'riah somewhat during Chhm Based upon mishna in Elu m'galchin
ONLY relatives over whom one must mourn, plus Hacham, Adam Kasher....
Bnei Ashk'naz [IE "Yekkes"] only tear for parents on Chol hamoed..
MB 15 Concludes: following Rema
"Where there is no clear minhag we tear on behalf of all of them [IE the ones enumerated by the m'chabeir] because that is the "Iqqar Hadin"
Implying where there IS a clear Minhag to the contrary that Minhag DOES Override "Iqqar Hadin" - [at least in this matter and probably for all laws of Aveilut]
We cannot CHOOSE this Minhag, however. The default IS indeed "iqqar hadin". We must acquire the minhag as a bona fide b'nei Ashk'naz [or another place with this Minhag]
How that happens is a subject for a future post BEH.