Hi there!
As a professional PrestaShop I am absolutely fine with your all requirements like- adding a new field in the registration form and make it dropdown in backoffice with some small fixing . I am the developer of many of popular modules and theme. So I know the standard coding on PrestaShop and I always follow the standard code according to PrestaShop.
Please have a look my portfolio and feedback from my previous clients:
https://www.freelancer.com/u/ranjudhk
==========Why Should Hire Me==========
1) I have proven experience, As proof, I can mention that I have already developed many of modules for PrestaShop.
2) All my previous client gave 5.0/ 5.0 rating,
3) You will get after-sale support from me for a certain period.
4) You find me on messengers for quick communication when you need
5) I will provide you well documentation what I do, for you better understand and future track
Please invite me to chat box for more details on your project like-time, quote, etc.
I am waiting for your quick response.
Kind Regards,
Ranju