1. I have downloaded a map, what/where path should i install it?
It depends for which version off the game and which map you have. If the map comes with an .exe installer or just an .m3d.
If it is an installer and its for Napoleonic wars then the default folder path to pick on the installer is C:/Program Files/Cossacks II/Data
If it is an installer and its for Battle for Europe then the default folder path to pick on the installer is C:/Program Files/Cossacks II/Run (is this right Daddio, havent installed maps on BFE for a while)
If it is just an m3d then its closely related to:
2. If ever an existing map will be modified, should saving it to a different filename work?
For this I'm going to refer to:
In short, if an existing map is to be modified AND you want to play online with other people with it, then it HAS to be renamed or you will have synchronisation errors. If an existing map is modified, then you can choose to install manually as described in above link or use on off the tools to create an installer for distribution.
So just saving it to a different name will not make it show up in the skirmish map list. It has to be properly installed in the various files.
Hope that made sense.