Personal Residence Mortgage Question - Duplex

[Account Closed]

I am considering buying a duplex with one side occupied, one side vacant. The current seller is leaving one side vacant in case an interested buyer would like to live in one side. I currently do not own a home or any other properties, so this will be my first. 

Here is my question - If I move in to the duplex property, I can get great financing with a Primary Residence mortgage loan. However, I do not plan to stay living in this duplex property very long because I am currently looking for a single family home for myself (to live in) as well. My bank has assured me that as long as I move into the duplex for at least several months, I can "change my mind" about living there, and still purchase a different home using another primary residence mortgage loan without putting my duplex financing in jeopardy.

Does this sound accurate? Does anyone have any experience with this? I always read that I must be in the property at least 12 months before I can purchase a different primary residence. Obviously, I do not want to commit mortgage fraud or do anything else that could cause legal trouble. 

Thanks in advance!