I would say it depends on whether you're talking about buy and hold = 100% stocks or being diversified in F and G as well, and that would be considered rebalancing as long as they stay constant - or close to it. Because changing those percentages, wouldn't really be considered buy and hold, but rather market timing.
The reason I say that is that nasa wouldn't have had a 13% loss in 2008 being fully invested. With C, S, and I losing 37%, 38%, and 42% respectively that year, that means there was some market timing / skill involved and that is not buying and holding. Capitulating to a buy and hold after a 12 year bull market sounds toppy to me.
Those negative 30% plus years, and we've had a few - although not for 12 years, can kill an account.