Add custom attribute on Account

I search a procedure to add some new attribute on Account or other entity.
I find you have to modify the zimbra-attrs.xml file to add it at the end of this file
but i thick is not really recommended for the future update

do you think the best practice is to add some new fields "attribute" is to create a custom db with all your modification
for make sure you not make some problem with Zimbra update or you have a better idea ?

Thank for your suggestion