Ok, I FINALLY figured it out.
Here's what to do:
- Find your wanted chrome extension (I'll use PreMiD for example)
- Copy the link
- Go to Chrome Extension Downloader
- Click download. Then .CRX file will download.
- Go to CRX Extractor
- Select your downloaded .CRX file from your computer, or drag and drop
- Click "Get Source Code". A .ZIP file with raw exntension file will start downloading
- Unpack it to whatever location you like (eg. desktop)
- Go to
opera://extensions, switch on "Developer mode" in the top right corner, click on "Load unpacked", search for upacked .CRX extension folder and select it
Hope it'll help some other people with this problem.