You only need to segregate the emergency load from non-emergency for an ATS/automatic-start generator. It's acceptable for an MTS/manual-start that the homeowner manually load-shed and open certain breakers.
In fact, you don't necessarily even need a physical MTS- you can often get metal interlocks (just a sliding piece of sheet metal) that fit over your panel and prevent the generator breaker from being closed until the main breaker is opened.
