Mrs. RustingInSeattle & the Rustettes change their RETURN date on average of once per year (for free). Just call the main number in Taipei if needed - most of EVA's fares should (hopefully) qualify for free changes as long as there is availability on the days you want to fly. And yes, the B fare bucket is an economy (not economy deluxe) bucket.

Note: Changing the OUTBOUND date does require fees - generally they just cancel the ticket (maybe a $250 fee?) and reissue. But the return has always been free in our experiences (your ticket may be different though).