Short answer
Permissible customs can generally be followed when they do not contradict Islamic teachings or involve injustice.
Islamic Guidance
What Islam teaches
Islam recognises permissible custom while prohibiting practices involving haram, oppression, extravagance or unlawful financial demands.
Practical Guidance
What you can consider
Ask whether a custom is genuinely Islamic, merely cultural, financially burdensome or harmful before adopting it.
Sources
Qur'an 7:31; Qur'an 5:2; Qur'an 2:188.