house hacking question

[Ockert Kruger]

the idea behind 'house hacking' is you move into the house/mfh in order to get a better interest rate, but when you move to the next place won't the bank change your mortgage to an investment property after 5 years when you need to reapply? or does this assume you take a fixed mortgage for 25 years - although I've seen experienced people say that variable interest usually saves you more than fixed.