you should make a chemical x that the player can drink or use in a command where when you use the effect it will open a gui for the player to customize the mutant verision of him/herself. please take this in to considiration
i have a few suggestions for the witchery mod
1.a key to transform into whatever you are(werewolf etc) whenever you want rather than having a timing for transforming
2. a character customization for when you become a werewolf etc.
4 keep it at 1.7.10 because no one uses 1.8