I'm thinking about applying for the 1 year Kellogg MBA ...
I'm wondering that after I'm accepted, if I could change from a 1 year to a 2 year program before and/or during the program.
Generally, I'd tell you not to expect it to be easy. Otherwise you'd have people switching halfway through, class sizes moving around, orientation programs that dont cover the same materials, etc. Its the same reason they dont let part timers switch into the full time program (they actually have to apply like anyone else).