[Junket]

It works the way you want in koreader. In the Kindle UI you don't get a hyperlink i.e. clickable link since the html page was renamed to .txt and Kindle is now treating it as a text document.

A workaround for this might be to leave the document name unchanged i.e. put the somedocument.html file into the Kindle documents directory. Then open the experimental browser and enter the url in the address bar

file:///mnt/us/documents/somedocument.html

And it will then display in the browser with a clickable link to the referenced local file. Note that the Kindle library won't include .html documents. The referenced file can be .txt, but the page with the link(s) needs to be .html if you want a clickable link to display in the Kindle UI.

A much better experience in koreader which will show the document in the library and parse hyperlinks for .txt or .html documents. But the workaround may serve your needs.