I have a level 8-10 party some dual class.
If i enter a town and put them in the Inn then save roster.dat out and uninstall/reinstall and then copy back in the above roster.dat, will those "better" characters be available??
Yeah I know...I know.. doing this would be like using a party editor but i am just interested... maybe try tonight and let you know, unless any of you guys have been there...done that??

Mucking about with your files is unnessary. The game has a built-in feature to restart the game while keeping your more advanced characters. It's under the Options screen.