With some inputs from Kilo and Face, the following seems to be a pretty reliable way of adding 'addactions'.
waitUntil{!isNull (uiNameSpace getVariable ["EPOCH_loadingScreen", displayNull])};
waitUntil{isNull (uiNameSpace getVariable "EPOCH_loadingScreen")};
//waituntil {!isnull (finddisplay 46)};
//waituntil {player == player};
sleep 10;
player addaction [("<t color=""#1376e5"">" + ("FuMS Admin") +"</t>"),FuMS_AdminMenu,"",5,false,true,"",""];
while {true} do
{
waitUntil {!alive player};
// uh oh...
waitUntil {alive player};
player addaction [("<t color=""#1376e5"">" + ("FuMS Admin") +"</t>"),FuMS_AdminMenu,"",5,false,true,"",""];
};
not even sure the sleep 10 is needed, but after adding the wait's to look for the drop in the loadscreen interface, things seem to be a lot more reliable.
Of note ***I am told**** addaction is an autoban under most security addons, so if you want this functionality for the general player, there is probably a little more work to be done.