function Modify_Enable_PlayerIssueRetreat(playerid, value)
	
	if value == true then
		value = 1
	elseif value == false then
		value = 0
	end
	
	-- create the appropriate modifier
	local modifier = Modifier_Create(MAT_Player, "modifiers\\enable_player_issue_retreat.lua", MUT_Enable, false, value, "")
	Modifier_ApplyToPlayer( modifier, playerid )
	
end
Example of use:
Modify_Enable_PlayerIssueRetreat(player1, true)
I tried using this, but it gives me a Fatal error.
SCAR ERROR Callstack: 
   C               [C]                            Ln   -1 (Modifier_Create)
  Lua             test.scar"]                    Ln  337 (Modify_Enable_PlayerIssueRetreat)
  Lua             test.scar"]                    Ln   47 (OnInit)
GameObj:
nFatalScarError: [Invalid parameter 5 (type expected=float, received=nil) in function Modifier_Create
  Lua             test.scar"]                    Ln  337 (Modify_Enable_PlayerIssueRetreat)
  Lua             test.scar"]                    Ln   47 (OnInit)
]
function Modify_Enable_PlayerIssueRetreat(playerid, value)
	if value == true then
		value = 1
	elseif value == false then
		value = 0
	end
	
	-- Create the appropriate modifier
	local modifier = Modifier_Create(MAT_Player, "modifiers\\enable_player_issue_retreat.lua", MUT_Enable, false, value, "")
	Modifier_ApplyToPlayer(modifier, playerid)
end
function BaseBuild()
	Modify_Enable_PlayerIssueRetreat(player1, true)
	Camera_MoveTo(mkr_camerabase, true, SLOW_CAMERA_PANNING, true, true); 
	Game_FadeToBlack(FADE_OUT, 0)
	EGroup_DeSpawn(firstbase);
	Rule_AddOneShot(OBJ_Farm_Mission, 2);
	Rule_AddOneShot(CP_Meter, 1)
	Rule_AddOneShot(BaseStart, 1)
	Rule_AddOneShot(NoRetreat, 1)
function NoRetreat()
	Modify_Enable_PlayerIssueRetreat(player1, false)
end