HI MIke
When you say toggle dimension style, I am assuming you mean changing the units of the Revit project? Is that correct? If it is, please take a look at the ProjectUnit SDK sample which shows how to set a unit to another unit and format.
From the UI, I can see that when I change the Project units for say length, I can see that the dimension in the model changes from say mm to inches - which seems to be what you are asking for too.
hope this helps
Saikat
Saikat Bhattacharya
Senior Manager - Technology Consulting