As far as I am aware lava...you could potentially patch in updates without destroying save games...I will have to check on this to be sure.
Things that will blow up a save game are when you remove information from a map.
For instance, if you had a tree object on your first map and in your revamp you deleted the tree, the game would crash once you loaded a save game and tried to reach that map.
Adding new information to existing maps is ok, however modifying certain things won't work either.
New information, such as adding new items or objects is fine, as long as you are not overwriting existing data.
Changing information that would be held in a save game won't work either, it will not crash the save game, but the changes will not all take affect.
For example, suppose you have a chest or a shop that has a certain item in it. Once a save game records that information (what is available in the shop and what is in the chests) then you cannot change this. It will hold the information that it finds when it firsts opens a map.
Now, as for additions, you should be fine...you would simply want to add new maps etc, then the save game should work because it hadnt written any information about the unvisited maps into the save game file.
The only thing you may need to watch out for if you are going to just add entirely new maps, is the warp player events to get your character there. You may have to account for future maps by at least putting up the warping object in the map you reach all the others from. For example, in your current game, if your final map was say map 5, and you wanted to have an expansion pack with 3 more maps, and you reach map 6 from map 5, you would likely want to add a dummy object where your warping event object will be placed to get the player to map 6 upon finishing up.
I hope what I am saying isnt confusing hehe. And I hope its accurate!
