Ok so you can’t load an acad 2010 cuix file into acad 2009.
 
Does anybody know if this will work…
 
Zip 2010 cuix file and extract the individual files,
Do the same with 2009 cui file,
Open the files I want to change and simply copy + paste the 2009 cui file data and past into the 2010 cuix file (replacing the 2010 info)
Then re-zip 2010 file and save as cuix
Re-load in 2009
 
Or is it likely to cause problems?
 
Ta

Unfortunately CUI files (XML-based) are not downwards compatible. You would need to redo your menus.