Apologies if this is a dumb question.
When I am connected to the internet, whenever I select a web-archive item in DT, it automatically reloads the page.
Most of the time, I don’t actually want it to do this.
Is there a way to turn off this behaviour? I would like to be able to reload pages when I want to, but don’t want it to happen by default.
Not unless you disconnect from the Internet, no. This is a byproduct of the dynamically loading data on the page. It’s being served from other locations.
If you want a static version of a web page, then save the page as PDF.
A webarchive normally does not reload by itself. If you view the webarchive of a plain static page it will show the page without reloading it from the server.
This means you have in your database the version of the page at the time of importing. (Additional note: The full text of this local page is the one which is used by DTP’s search engine.)
The version on the remote server might have changed. If you want to view the current remote version you can press the reload icon in DTP. (But be aware that the new content will not be searched by DTP!)