Hello,
My name is Pajam and I am web developer from Sweden. I have worked with PrestaShop since version 1.5 and hence have a lot of experience with it. I have also had multiple shops of my own on PrestaShop.
I have read your description and I suggest that we make a custom module for this in order to ensure compatibility with other modules, modules you might install in future, upgrades etc.
Are you running version 1.6 or 1.7?
Looking forward to hear back from you soon!