There is no way in hell you are going to get the whole network to simultaneously re-define a bitcoin. Dumbest idea I've heard in a while.
It doesn't have to be simultaneously if we introduce a new name/symbol equal in value to current bitcoin (100M satoshis). We can call it megabit, megabitcoin (M
BTC), ZIB or something else.
In a few months, we can switch completely to (redefined) bitcoin and drop or leave the name for 1M units.
No problems at all.