What is the importance of wallpaper paste when glueing a project?
I am going to glue some tissue paper onto a polymer clay bead. The glue recipe calls for 1 part wallpaper paste, 1/2 part Elmer’s glue and 1/2 part water.
I dont have wallpaper paste… Would it be ok to just use a glue/water mix (thicker than paper mache glue) Planning on coating the bead with a varnish after the tissue paper is glued.

Yes. I’ve never heard of wallpaper paste being used like this. A mixture of Elmer’s or PVA and water should be fine.