Not quite! A few months ago I read a thread by Balthagor explaining how you can do it. Move your save game file to the Multiplayer file and load the game as the target country-B whose borders that you wish to change and set his military so that they won't react and declare war on country-A, save game and start as the country-A move your units into the border regions of country-B so as to annex the territory that you want. Save game and move back into the folder that you started with then you can make your Cache file.
It would not be so hard to mod this in, but it takes time since it is large project, you would have to make a new .UNIT file that has units from RA3 and not real world units, new maps(groupings) tech levels and other country data, remaking of the map(groupings, limiting the map to 3 worlds and add/delete cities/facilities etc), new leaders, new flags, new scenarios, new texts etc.
V1.2.406 has been released! -> End of an EraLinks: List of Mods