What i would do is create a group action called RATING MM to RATING CONVERSION and vice-versa.
To do this create and action to format the RATING with the RATING MM value, then change that value e.g. 0.5 to 10 and so on...
Continue to do this with RATING MM values from 2.0 to 5.0.
I hope this works. I'm on my phone ATM so havent had a chance to test this.
If it does then repeat a similar process called 'RATING to RATING MM CONVERSION'
It stores it in the itunes 'Library.xml' file. I noticed to my despair before transfering songs which had there stars shown that they no longer had them on a newly formated HD. But there is ways round that by keeping the same root drive and folder structure for your tunes and then loading the pre saved .xml into itunes.
But I decided instead to simply put the rating 0-6 (6 for bangers in the COMMENT tag. That way every programme can see it. An e.g. of my COMMENT tag would be '5 - 2A' So the '5' is the rating and the '2A' is the key of the song. Put this with itunes smartlist and BOOM a very organised collection.