You cannot change the text of a marker, you can however switch whther a marker is visible with:
makerNamer setMarkerType "empty"
that will make it invisible. To change it back switch empty with one of the following:
"Flag", "Flag1", "Dot", "Destroy", "Start", "End", "Warning", "Join", "Pickup", "Unknown", "Marker", "Arrow", "Empty".
This way you can create multiple markers with different text but only show the marker you want to be shown at a certain time.
Also, use setMarkerPos (getPos player) to mark the player's position on the map with it. You will obviously need a loop to make sure it updates his position.