Redesigns are free! And, if it gets upgraded, you can always redesign later (doesn't have to be within the 48 hours) if you keep up with the proof! ^^
thank you! also, one more question- do extra limbs include tails? (i want to do two shrimp tails)
Unfortunately no, limbs only apply to arms and legs!
However, if you are able to get an Ancient MYO sometime and you roll the mutation "Duplicate Body Mod," it allows you to do so, so you might want to pocket that idea!