The question is still there. Is it possible to mod memory voltage (not core or aux voltage) on Hawaii via bios editing?
Memory voltage (ie MVDDC) can not changed by bios modification.
IR3567B on Hawaii / Grenada controls VDDC (core) / VDDCI (aux) only.
Only cards which allow software manipulation of MVDDC "out of the box" are Asus 290X Matrix and MSI 290X Lightning, which I don't think most would buy here given the context of use on this forum. So far I have not seen any R9 300 series cards with MVDDC "out of the box".
MVDDC can only be changed with "hard vmod", google the terms
290x mods - kingpincooling.com 1st hit is correct link, in 1st post 1st link is document showing "hard vmod". In this
post by The Stilt you'll see it may yield you only small power usage drop.