Hey Cablenexus,
Im not 100% sure now but i think i did protoype modding. I used my own mod and scenario file, created for that a new mod folder and bound the scenario/save game to the new mod. Any new stuff, additions or changes would come into that new mod file except for the map changes where i currently use the save game.
Okay and for the map, to edit its size i did the following:
1. Made a savegame of Ancient Mediterranean in turn 1
2. I checked how the tiles are saved in the scenario files. If you dont know how:
they are saved in a 2 dimensional array where the Y-axis is saved in the first dimension and the x-axis in the second dimension for example like this: tile[2][10], meaning the tile at y=2 and x=10.
In the scenario file this mechanic is implemented this way:
You will have to look for the <chart> entry. Subordinate to <chart> you will find as many <ArrayOfChartSquareMemento> entries as the map's size in Y. So the Ancient Mediterranean scenario will have 44 entries of <ArrayOfChartSquareMemento>, as its total size is y=44 and btw x=88.
It is saved in the order as it is presented in game, meaning the first entry of <ArrayOfChartSquareMemento> is the first top row of the map.
Now if you open the first <ArrayOfChartSquareMemento> in the scenario file you will see a list of all 88 Tiles of the first top row of the map. ( where each tile's informations are saved in <ChartSquareMemento> ). So the complete map got 44 <ArrayOfChartSquareMemento> entries each with 88 entries of <ChartSquareMemento>
3. Knowing about how the map is implemented i made a new map in the scenario editor 88 tiles wide(the important number here) with water( you can use any terrain you want, i wanted to add only water tiles to the XL scenario)
So i saved the water scenario, opened it in notepad++ and copied some of it's <ArrayOfChartSquareMemento> entries, and pasted them into my XL scenario file right in front of all other <ArrayOfChartSquareMemento> entries. I then loaded the scenario and those water tiles were added to the top of the map. I tested a little time how many Y i would need to include France and Britain. At the end i copy-pasted 24 elements.
4. Then there was a problem: I only wanted to expand the Ancient Mediterranean scenario and not build it complete new. BUT with the new map additions at the TOP of the map all original Y-positions of units, cities and mines were obsolete e.g. a city in the original scenario at y 10 and X10 would be on my map on a water tile. Meaning all units are 24 Y positions off their intented positions. And there comes the last point.
5. So if you want to change the map size of a scenario but keep all units, cities and mines, you will need to adjust the Y positions of all units in the scenario file. To be said, you dont have to do that, if you add new map parts at the bottom of the map! As just for info, if you want to add map to the left or right on the X-axis, you wont need to adjust the X positions of units if you add it to the most right of the map. You need to adjust it if you add map on any other position.
Never the less, a crazy task to adjust the Y value of all units on the map, if you would do it manually one by one.
Im sure there are easier ways to do this but to make it a fast task i created a temporary xml file and copied ALL <UnitMemento> entries into it. Not anything else.
I then started to use the find and replace function and had in mind to replace ALL original Y values by its original value +24, to get all units back into its intented position on the map. Because the old map got an Y value of 44, all units must be within this range and i only need to search and replace within this range. But i had to start within the range between 24 and 44 to avoid adding up the y-Postion of units between 0 and 22 twice during the process of finding and replacing.
It looked as an example like this: Find " y=24" and replace with " y=48" .
When all units Y positions were corrected, i copy pasted the <UnitMemento> entries back to the scenario files and all units are back in its intented positions.
edit: i just noticed after loading the scenario as a game i have to edit some more values. I will add this info when im done.
edit2: I had to adjust the playervisibility as well by adding 24 lines before each players <visibility> entry. I guess winningpoints as well, i will do that tomorrow.
Alright, i will enter the steamworkshop/discussion forum for mods on steam then. Thanks for offering help, or even joining at some time

.
This is what i did today: i finished the total terrain for france but had to decrease the height of the north borders of france/germany, poland. The old borders let the countries be too big but now its scaled better. Next i need to research the biggest celtic tribes for France and Britain. I found some maps but there are just too many small tribes, too much for the scenario. Maybe in total +4 tribes in France and England....... If i remember right in a Total War game you could select the Britons as the tribe to play in england. This and maybe Picts in scotland may be a solution for England. Any knowledge or ideas are welcome

. Of course theres google, but up to now i had no real catches.