Is it possible ti edit Mark points ?

When I create a Mark point, select it, and then press "Data", makes the UFC indicate "M 2", I then press ODU POS, enter LAT, press POS and enter LON.

This though creates a new waypoint instead of editing the Mark point.

Also (as reported elsewhere) I cannot change the elevation.

Maybe Mark points aren´t meant to be edited !

Maybe Mark points aren´t meant to be edited !

This, pretty much. If you need a Target designation from the Mark, you either create a Waypoint from it or use it directly. Markponts are limited and cycle through the latest created when the last is reached, overwriting it.