Why is it that Non-Metal bands that have a "Changed Name" status (with an active band name on this site) non-acceptable? Or an active band that has acceptable metal music under a different name? For example, In Reference to a Sinking Ship (Pre-Dark Sermon) or Death Piggy (Pre-GWAR) is not Metal, but eventually change their style to Metal under a different name; is there a reason as to why this is not acceptable?

Name changes are considered separate entities by the site, and just like any band (with some exceptions), they'd have to be metal to be on here.

Even through it's still technically the same band?

Yep, and even if they were metal, they'd still need a valid release.