Applying same change to multiple map documents?

The most efficient way to make bulk changes to multiple documents is to use Python scripting available in ArcGIS. You would need to write a Python script that will iterate (or go through) each of the map document files you have and apply the changes you specify in the code.

Start looking for the arcpy.mapping module. 10.1 and 10.2 have more functions embedded but you can go a long way even with 10.0. Specify what type of changes you need to perform and then see if you can find the matching functions within the arcpy.mapping module. If there are some that are missing, start a new question and we will try to find an alternative. If you have not scripted in ArcGIS before, consider reading through the getting started help.

Also consider taking a look at arcpy.mapping sample scripts which Esri staff put available online for download (with source code). According to the help file, they should work for 10.0, but I have used them only in 10.1 and 10.2.

PS. Start with just one map document to see if the changes are applied correctly and always back up your data before making any changes.

Have you every used Data Driven Pages? Not sure if version 10 has it, I am using 10.1. Pretty slick, but would be after the fact for you at this point.

Data driven pages will move from one area to the next plotting or exporting the maps as it goes. I layout out one large watershed and then define the sub-watersheds within for the individual layout limits.

Do a search in the help for Data Driven Pages for more instructions.