It would have been easier and safer to just copy the original file... Windoze Copy/Paste for text might add format data, or change line endings, for example.
Also, you must use a pure text editor to edit such files (not a word processor).
Ah, oh, good to know! I wasn't aware of it. I may try to replicate it again as I actually did copy and paste the original file, first. Then edited the width with notepad++ in the automatically detected xml-format layout and saved it... I will try it again, maybe their went something wrong the first time that I'm not aware of.
The XUI file format is extremely strict (like any XML format): any typo (missing space between a closing quote and the next attribute name, missing or extra slash, missing or extra angle bracket, missing or extra quote, bad attribute name, invalid or XML-reserved character), and your are hosed (and could possibly crash the viewer)... There is little to no safety check done for that format in the viewer code (those files are supposed to be bug-free), so your file must be perfectly formatted.