So I know this is a bit of a weird thing because typically there isn't any reason for a race to give set ability scores, however, one of my players wants to be an awakened animal. I have worked out the mechanics of how this can work, but it isn't letting me do what I need to.

Basically, I want to set all the ability scores and then my player has the option to make either Int, Wis, or Cha a higher number set number so they can take the spellcasting class they want.

Is this something I can do? Or is there even some kind of crazy workaround? 

Thanks in advance for any advice :)

The one workaround so crazy it just might work is if you write it very clearly in text and trust your player to follow instructions.

Edit: In other words, the fixed ability scores are impossible, that would have to be the honor system trusting the the set their base stats the same. The choice of a buff to one of the three Spellcasting abilities you would do with Options. I explain them in these threads:

• https://www.dndbeyond.com/forums/dungeons-dragons-discussion/homebrew-house-rules/67361-subclass-help#c4
• https://www.dndbeyond.com/forums/dungeons-dragons-discussion/homebrew-house-rules/68126-subclass-options-not-working?comment=2

Darn, I was afraid that was going to be the case :(

Thank you for the info though. I will do just that. Luckily it is a player I fully trust to not be shady so we should be okay.