ROX-Filer gives my ActionScript files (hence having the .as extension) spreadsheet icons, apparently because it is configured to think Applix Spreadsheets use that extension. How can I change this?

Using the ROX Mime-Editor I added the type "text/x-actionscript" and specified it as matching files with the name *.as. However, ROX's behavior was unaffected. I then tried setting the "Contents matching" priority to 100 for text/x-actionscript, and to 0 for application/x-applix-spreadsheet. Still no effect. I would delete the Applix mime type, but I'm not allowed to remove any information that I did not specify myself.

When you right-click and go to properties what does it say under type ? is it 'text/x-actionscript' ? If so go to '~/.config/rox.sourceforge.net/MIME-types', make a new file or edit 'text_x-actionscript' to run whatever program you want when you click it. Look at the others for an example.

No, that's the problem: under type it says "application/x-applix-spreadsheet".