I tried it in two ways. I can see that script changes their position but they somehow lose the syncer instantly and become immortal again.
Here are the ways I tried:
addEvent( "456", true )
function updatePosition(ped)
if not getElementSyncer(ped) then
local x, y, z = getElementPosition(ped)
setElementPosition(ped, x+2, y+2, z+2)
end
end
addEventHandler ( "456", getRootElement(), updatePosition )
addEvent( "123", true )
function updateSyncer(ped, target)
setElementSyncer ( ped, target )
end
addEventHandler ( "123", getRootElement(), updateSyncer )