A Homebrewers’ “How-To” FAQ*

Just to save y'all the trouble, you cannot have the homebrew subspecies be nested under the homebrew species the way official stuff are.

You can make a subspecies of an official race and do it but not for homebrew species. That has never been a thing and is unlikely to become a thing due to D&D 5.5e moving away from subspecies.

Your best alternative is using the Options system to set the subspecies as Options instead of being set as subspecies - this is the way new 5.5e does them now, such as 5.5e version of Elf or Tiefling.

but for 17 what if the spells are already in an option like for tieflings you can choose your spellcasting abillity but you get different spells based on your legacy???