Here are all the codes that you can use on the maps, in case you forget again:
There's more off them but they dont relate to map making.
On your issue with the existing mission map:
Those ID points are linked up to the script which runs the mission. It is very likely that changing or deleting half or none off them will cause unexpected gameplay while trying to play the map as a "skirmish" map, such as defeats and other oddities.
It is however possible to clean out the scrips and related links on the map itself as shows on your picture. A proper clean out will result in a blank map which should be playable as a skirmish map.
I haven't had time to finish writing down all information on how to set up scripts for mission and how to get rid off them, though there is some information that might get you started to clean up the map you would like on these pages:
What you see on your picture is a node, it is used for a variety off things to set up the scripts.
Read a bit here to get an idea off how to access the node menu:
There is a drop down menu where , after selecting the node, you can DELETE it.
If you are on BFE, you might need this file in order to access th CTRL +E Advanced Editors:
Note, that besides Nodes, there may be other things on the map, such as vGroups, Edges, Camera Points,... they would all need to be deleted to ensure the map plays normal and not in mission mode.
Moreover, you will also have to delete the scripts itself to which these nodes are linked up, or the script will still run and try to find these points on the map.
You can choose to clean out the script itself trough the BattleHandler, Script Handler or MainBeScript or delete the link to the custom script in the map options.
I'm well aware this may somewhat be confusing to try out and may be quite a lot off work, but just remember that everything that has been added to the map, can be deleted as the developpers started with a blank map aswell.
Hope this helps, and don't hesitate to ask more question on deleting something specific if you run in to problems.