Slitherine

Existing scenario has Human A and B
If i want to "transfer" B to A, must i link each specific hexes and units in the mission or is there any easier solution?

You need to edit the set up of the team/factions. That is easy.
But many of the objectives and their triggers will now point to the wrong team/faction. This will take more effort to fix.
Perfectly doable, though.