Least Difference and MIMU

1. Take the ten digits from zero to nine. Arrange them in two numbers. Subtract the smaller number from the larger one to get the least possible difference.

2. Consider the following four rules:
   1. You can add 'I' at the end of a string ending with 'U'
   2. If you have a string Mx you can write the string Mxx
   3. Whenever you find a 'III' you can turn it into 'U'
   4. Whenever you find a 'UU' you can remove it from the string
   Are you able to turn MI into MU?