The phrase "also the custom of" is correct and usable in written English.
It can be used when discussing traditions or practices that are common in a particular context or culture.
Example: "In this region, also the custom of celebrating harvest festivals is deeply rooted in the community's traditions."
Alternatives: "as well as the tradition of" or "in addition to the practice of".
He also opposes the custom of appointing the chief justice on the basis of seniority.
Also, beware the custom of putting drinks in paper bags to disguise that you're drinking an alcoholic beverage.
Ndebele also practice the custom of levirate, in which men are obligated to support the wives and children of their deceased brothers.
He also devised the custom of hosting periodic Friday evening soirees, inviting students to his home just to be sociable over wine, and take the edge off the week.
She has also challenged the custom of recent years to segregate medical treatment: female doctors for female patients, male doctors for male patients.
Pliny also describes the custom of having a bust-portrait of an ancestor painted on a round bronze shield (clipeus), and having it hung in a temple or other public place.
In the Rich wealth class, some noble women (although very few in our study population) might have also adopted the custom of hiring wet nurses to breast-feed their babies [33], resulting in shorter inter-birth intervals and higher fertility [34].
It also pointed to the custom of "lopping" applicants near the end of the process while admission officers are shown a spreadsheet that "prominently displays applicants' races". And it argued that Harvard has "never engaged" in a good-faith consideration of race-neutral alternatives.
Mr. Kean also has attacked the custom of senatorial courtesy as "pernicious". He said dozens of his appointments to various boards and commissions were being held up by a number of senators, but that these appointments usually did not attract the public notice that a judicial nomination did.
There are also areas where the custom of smoking Western cigarettes has followed the pre-existing smoking of native tobacco with this probably facilitating the uptake of the new habit.
