They are a bit of a pain to reroot as the holes for the eyelashes are tricky. Have you already got one without eye lashes, I take it?
I think the eyelashes are probably kanekalon rather than traditional nylon - if you reroot them with nylon you may struggle to get them as thick and curly as the original [although thats maybe not a bad thing
] As you are rerooting with a thinner hair, I would just make sure to reroot with hanks which look too thick for the hole as you will need to get a good cross over to ensure it looks natural. There are a couple of good Sindy and Barbie eye lash tutorials about which will probably help you out. I am sure I have one in my favourites if you need it.