Are the banding rules changed with flanking?
No. One creature can only be assigned to block one other creature (Mirage rulebook, p. 50), and banding doesn’t change that. You still have to assign a blocking creature to block one specific member of a band. Although that blocking creature will block the entire attacking band, it’s only assigned to block one member of that band, so unless you assign your creature to block the flanking one, the flanking will not have an effect. On the other hand, if you block a band that has Thicket Basilisk, the Basilisk’s ability will still take effect, as it depends on whether or not it’s blocked, not whether or not a creature is assigned to block it specifically.
