It's stated that the link element must be embedded in the head section.
I need to link some style sheets to a document with static predefined header (rendered by legacy framework). So I can't insert the tags to the head. Can placing them outside cause issues with any browsers ? Or maybe its better to insert the tags with javascript ?
No version of HTML allows it, but browsers perform a great deal of error recovery. I wouldn't depend on it.
Don't do it especially on a website as opposed to a intranet. You will start to limit what browsers can view your site correctly. Please could you elaborate on your usage, I bet there is a better solution to the problem you are trying to solve.