Demellion
To accomplish getting the altitude of a marker before the alternative syntax introduced in A3 v1.93, you can do a workaround using setMarkerDir as it accepts any number (above 360 or below -360):
"myMarker" setMarkerPos [200, 200];
"myMarker" setMarkerDir 1640;
After, setting player position as an example:
player setPosASL [(markerPos "myMarker") select 0, (markerPos "myMarker") select 1, (markerDir "myMarker")]