Theme update and file modified flag - how to reset it?

[billium]

I have a Dawn V6 theme that I want to update to V7 but the 'new version' message is hidden - presumably because I made a small mod to theme.liquid  so the code is considered changed. That file does display the modified dot next to the name.

So, I undid my code mod putting the file back to as-new but it remains 'modified' and see no way to unmodify it.

How can I tell ( or trick) Spotify into considering the file unmodified so hopefully it allows me to update the theme automatically ?