I had mentioned in my September 10th post on file type detection that you couldn't change the encoding on a pending add, without undoing the add and re-adding it.  While it won't work in beta 3 or beta 3 refresh, you'll be able to change the encoding on a pending add in the next public release.  That means you can use the edit command with /type option from the command line or the properties dialog in the GUI to tweak the encoding before checking it in.