query about class diagrams (for all u software engineers out there)

[nattylife]

if im doin a class diagram and theres a state change in my system during a scenario. do i want to include a class for that change (im doin a use case on vcrs and cant decide if i need to include the state change from regular vcr, to recording ready vcr)?
all in UML.
im split in half of what to do. and i cant find any specific info on class diagrams and state changes.