Hi, 

1- class ProductTemplate(models.Model): 

    _inherit = 'product.template'

2- make sure you add the module 'product' in depends in __manifest__.py

P.S : you don't need to create a Module just to inherit a form...

Thanks ibrahim i dont know what you mean I created the module for these changes. isnt it better to move on this path for these changes?

if i change the script on the existing documents wouldn't it create issues moving forward?