And if you want to do them flashbacks in a cutscene(cutscene=during mission) you could setpos the player and units to another location during the cutscene...
You can use the most common setpos commands:
Loon setPos [x,y,z]
and
Loon setPos getPos markername
the above codes if you only have one unit.
Or if you have a hwole group you want transfered you use this:
"(vehicle _X) setPos getMarkerPos {Marker}" forEach units groupname