We have 4000 users across 100 sites, all with roaming profiles. We are moving to local profiles as at slow sites it takes 20 mins to log in and out. Is it possible to write a program to swich the users from roaming to local ( i.e. to do "Control panel", "system","user profiles" tab, "change Type".)

It seems I don't need a program at all! Setting the user to use a local profile (by deleting the value in "profile path" for the user using active directory Users and Computers) causes any roaming profiles stored on PCs to become local, next time the user logs in. The reverse is also true - local profiles become roaming ones if the "profile path" is filled in.