I am currently developing an extension that is adding two select elements (City and District) that work the same way as the RegionUpdater. (When you choose a Country, the Region select populates, when you choose a Region the City select populates, etc...)
It is working fine, but now I would like to change all the address forms to make it appear everywhere.
I would like to make this extension available to everyone, so I would like to make it easy to integrate, and easy to modify. So what is the best practice ?
I will clearly not modify the template file from the default theme, but I was thinking about updating the layout, and changing all the template of an address form by the corresponding one in a folder of my extension, with the new fields added.
The main disadvantage is that if you are used to modify a certain template to modify the form, it will not work anymore.