To Volvie: you say based on local customs. How monolithic is any one locality? Do you mean as per the individual yeshiva?
If so, yeshivos may send the dress code info to the parents but do they post it on the yeshiva doors, i.e. don’t come in if you’re not wearing a white shirt, etc.?
Torah is a morasha to the entire kehillas Yaakov, when I last checked.