I'm with Felipe on this one.
In each selected space, the executing Faction places
1 of its Available Guerrillas or replaces 2 of its Guerrillas with 1 of
its Bases, within stacking (1.4.2). If the space already has at least 1
of that Faction’s Bases, the Faction may instead either:
Place a number of its Available Guerrillas up to the number of its
Bases there plus the space’s Population value (1.3.2-.3)
Move any of its Guerrillas from any spaces on the map to there
and flip all its Guerrillas there Underground (whether they moved
or not) (1.4.3).