Download Dictionary Text File and Add to Personal Word List?

I would like to download a more-comprehensive spellcheck dictionary in a text file format, massage it to match Scrivener’s format, and paste it into the Personal Word List file.

Anyone try something like that? Is it practical?

In response to a related question, MM suggested this:

I did this with complete success using a spelling list I had developed in another program.

That’s encouraging. Anybody do it with a full dictionary available online?