I would add, that once you create the .bmp file, it's easier to edit the .lst file in Notepad then using the in-game interface for each terrain. Look in the C:\Program Files\HTC\Aces High II\maps folder. Open it and you'll see something like this:
AirField Small,easy sfield.bmp
AirField Medium,easy mfield.bmp
AirField Large,easy lfield.bmp
Base - Vehicle,easy vfield.bmp
Base Port NW,easy Port NW.bmp
Base Port NE,easy Port NE.bmp
Base Port SW,easy Port SW.bmp
Base Port SE,easy Port SE.bmp
Fuel Gallons,Fuel Gallons.bmp
Normal - Town,town.bmp
Strat - AAA,aaafact.bmp
Strat - Ammo,ammofact.bmp
Strat - City,city.bmp
Strat - Headquaters,hq.bmp
Strat - Troops,barrfact.bmp
Strat - Radar,radrfact.bmp
Strat - Refinery,refinery.bmp
You can edit it and simply make copies for each terrain you want to use with your particular set of CBMs. When you pass around custom sets, include the .lst file and they'll automatically load with the appropriate terrain(s).
Save this to maps folder in AHII folder
http://files.filefront.com/notesbmp/;11784375;/fileinfo.html
you can modify it in paint using the text tool and change it to say anything. I have used it for things like object strength and dot commands
once you have saved your version to folder just go to game and pull up clipboard maps and click on add new map, select file and give it a name. now you will be able to see this in clipboard maps.
special note here though you will need to do this once for all the terrains that you use and the image size needs to stay 512x512.