I have a question too if i change from Maynard to Randy for exemple will the advance tech be unlocked ?

Changing storytellers did seem to allow advanced techs to be researched. I DID NOT see any other factions spawn in, but i also didn't try saving and reloading or anything like that (since i didn't actually want that in my play through.)

Edit
After looking at the FAQ I found this:

"Changing the storyteller to Maynard Medieval mid-save will not affect the factions since they are determined at world creation."

Based on this I think it's safe to assume the reverse is true as well.

Originally posted by Breislord:

has anyone tried changing from maynard to a different storyteller midgame? does doing so allow the outlander and pirate factions to appear?

Factions are generated at world creation, unless you have a mod like faction discovery they WILL NOT generate after that point no matter what. If you do have faction discovery I can't comment on whether or not the factions will spawn, but I am fairly sure faction discovery asks you before generating a faction, so you would still have control over it.