Just played around with it a bit...
You can export the effected scripts from 8.0 and import into 8.1 and it doesn't screw up the extended ascii. For GML in objects you can copy-paste into 8.1 fine. Bit of a pain, but after saving/loading it still looks ok.
EDIT - from release notes:
PLEASE NOTE: The Code Editor is now full unicode, however... this means that you WILL have to re-enter all your strings in order for them to work. This is because we have no idea what codepage they originally came from, so cannot patch up characters >127 into the correct unicode space. You can cut and paste them so that windows does this, but it's still going to be painful. Sorry....
-_-