I know that it's upsetting and baffling when a child acts out of character but don't lose heart. Even 'good' kids push boundaries.
You have identified frustration is a trigger. Acting out is often an attempt to seize control at times of stress or imminent change. Unless he has developed problems at school ie bullying his peers, so far he has limited throwing his weight around to the family, superiority over the weakest, ( his little sister).
Moving, a new school, a baby on the way, loss of a grandparent, one parent suddenly working away from home a lot or a home going up for sale and uncertainty about the new home can be unsettling. Or something apparently trivial. What seems like no big deal to us can be very much a big issue to a child.
When DS is calm try and have another go at talking. Striking up conversation can seem a bit phoney so, much as parents of teens do, have a go at airing topics while in the middle of a chore. Driving, or mucking out guinea pigs, or emptying the dishwasher. Or slapping paint on a big sheet of paper can reveal some anxieties.
"Little pitchers have big ears" they overhear snatches of adult conversations then dwell on issues and panic inwardly. Or we present them with a new idea, tell them how fantastic and exciting it is, without letting them digest and accept it, so they fret it's not all right and can't voice apprehension.
Ask his teacher how he is behaving at school. If you think this behaviour is now spilling into school life see if you can arrange some paediatric counselling but if there's a big move in the near future I appreciate that may not be possible.