An artist's depiction of an Extended Unit Death
I wonder if a map could make something display other graphics that already exist in the mod or Doodad graphics.
No, that isn't the case; any changes and implementations need to be integrated into the
mod, not the
map.
Think of it like this: The map holds some information that the game interprets. The game holds a
ton of information and knows how to interpret everything, such as what images/sprites to show for a certain unit type. If you want to display different graphics than what the game
knows what to render, you have to either:
1) Overwrite the section of the MPQ the game looks for to get the image
2) Overwrite the code pointing to where the game looks for that image
Notice that neither of these involves the map. These changes will apply across
all maps (i.e., it is
map agnostic).
Going back to this briefly:
By modding the map we can get more stuff without those stuff being a part of the mod itself, as some guys earlier said that it is possible.
Yes, you can theoretically put parts of your mod into a map and point the mod to that information. There's two and a half problems with this:
1) You gain absolutely nothing by doing this: you still have to write the same amount of modifications, and it would be much easier to just contain it all in the mod itself.
2) By doing this, you're making the game
unplayable for all maps that do not have that mod data. It's very likely that you'll end up with an unstable mod that crashes on all other maps.
3) This is an architectural disaster (read up on
Separation of Concerns,
Coupling and
Cohesion if you care about architecture).
In short: you should absolutely
not be considering putting mod data into a map. Completely disregard mapmaking for the scenario you're describing, because it's not practical and only worsens the potential outcome of your project.
So as for my answer to this:
if all graphics are done in a mod, could a map make it able to display a unit/building with graphics from an other unit/building?
I'm going to say no. The technical answer is yes, it is possible as long as you still have the mod wired up to interpret and use the data, but you can consider the answer to be pragmatically "no." Do this in your mod, not the map.