Extending fields / Adding custom fields to Manufacturers / Products | PS 1.7

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Hello,

I'm trying to find the right way to extend the available fields for manufacturers and products in PS 1.7.

After adding a field to the database in the right table I need some advice which files have to be modified to get it working with all PS feature i.e. translation and validation.

Plus I'm not sure if it's better to use a module or Overrides …

Thank you for every tutorial or list of files which are necessary to add custom fields!

PS 1.7.3.0 / custom template