The following modification isn't my idea. There are various Japanese language doll blogs which explain the exact same thing but they're entirely in Japanese. This might be the first English language blog to describe the procedure. At the very least, I hope it's the first.
If you've been frustrated with the range of movement your Dollfie Dream has with her legs, here's a mod for you.
If you own some version of a Dollfie Dream III or Sister, you might recognize this part as the chest and neck frame. I decided to run an experiment for increasing the movement range by putting together a custom neck joint.
EDIT: If you perform the procedure mentioned in this post, the masking solution will mix with the putty adhesive holding up the eyes. If you ever remove those eyes, you won't be able to reuse the putty adhesive. Yes, I learned this the hard way long after making this post.
Having a few ongoing simultaneous doll assembling projects, one cyborg I built was Platina. (Yes, I named her after the Valkyrie Profile character.)