First the aside....I TOTALLY know what you mean about some of the CRJ-200's having SUPER long seat belts...it is ironic since they have such small seats!

O.K. back on topic...

As others have pointed out...the rule is that exit row seats can NOT have seatbelt extenders...the logic being that in an evacuation the extra length of belt could get tangled and in the way of people trying to evacuate...

For how to handle the situation...it is tough because there isn't really a point in arguing/debating with the crew.....

Really your two choices were...moved seats..or wear the seatbelt for take off and landing and leave it unbelted as much as you could during the flight...

Seat belt length various A LOT, not just from one type of aircraft to another...but within aircraft types...the Delta 757-200s they got from TWO have SUPER small seat belts....

Some 757-200 from NWA have SHORTER seatbelts in FC than in coach....