Кто-нибудь работал с Magento extensions?

Это особенность установки расширения через Magento Connect (он же Magento Downloader, по-вашему). Нельзя установить расширение повторно, пока не удалишь файлы старого. И не важно как эти файлы туда попали изначально (через коннект или через фтп). Просто запрещено перезаписывать файлы при установке через Magento Connect.

Просто залейте ручками

Yes, being a professional Magento developer over the years. My core expertise the is with Magento where I am deploying all my eCommerce business strategies inclduing Ecommerce Plan, Design, Development, Marketing Strategies on client projects.
You can checkout my contribution on Magento Extension on Mconnect media website which is one of the leading Magento & Ecommerce Web Development in USA, INDIA.
You can also hire such Magento Developers like me for your future projects if needed.

It seems like you are stuck at some technical issues that's why i highly recommended you to consult with ecommerce expert instead of manual troubleshooting they will guide you at each steps to save your store from other troubles.

The Magento 2 Gift Card is a creative tool that allows customers to buy & send gift cards via email, printed, or offline method to their loved ones or use for themselves. This Magento 2 Gift Card Extension can Configure Gift Products, can create gift card products from Magento, and purchase from the site frontend.