In synthesizing PbS nanocrystals will there be any problems if I use lead IV acetate instead of lead II acetate?
You might run into problems. $\ce{Pb(OAc)4}$ is a pretty strong oxidant! 

What will be your sulfide source? Are you sure that it isn't oxidized these conditions?

Edit 1

At least N,N'-diarylthioureas are efficiently desulfurized by lead tetraacetate and furnish ureas (and sulfur) via a carbodiimide intermediate, see Bull.Chem. Soc. Jpn., 1984, 57, 315-316.

Edit 2
If you don't mind a personal advice: I wouldn't want to add complexity to the protocol just to maneuver around problems (and create others) I wouldn't have if I were using the right starting materials in the first. (The German term for that is verschlimmbessern, which translates to something like disimprove).