Pre-Request Checklist

• I have checked that I am on the latest version of Terra.
• I have searched github for similar features requests, including closed
  ones, and found none.
• I believe this is within the scope of Terra.
• This feature request is for all of Terra, and isn't something that
  should be implemented by a pack or addon.

Feature Description

Allow a config to be defined that maps removed biomes to valid registered biomes. Perhaps there would be a default mapping for Terra biomes that don't have a unique mapping defined.