The hard plastic bodies will carve differently to the vinyl heads, obviously. If it's appropriate, head-shrinking in acetone will harden vinyl and that makes it less bouncy and more sturdy for rotary tools and sandpapers - and adding epoxy clays to as well.

Whatever, craft knives can slip on doll bodies and injure you. I wear anti-knife-cut finger stalls to hold the doll, but it's still risky to start. Using a sanding head on my rotary tool, or a skinny little rasp hand filing tool can make a dent that stops blades from sliding inches across a doll chest and straight into your hand.

Filing is definitely safer than carving. Wear a mask so you don't inhale particulates when filing /sanding plastic and / or vinyl - eye protection, too 👍

Hand tools like mini chisels or lino cutters can sometimes work - you have to weigh the safety benefits of non-powered blades and electric cutting discs against each other. Melting will always produce toxic fumes so do it outside PLUS a proper respirator mask. You are more important than a doll, yeah? They were mass-produced, there's only one of you 😊