Is it possible to add Lua code to a window?

[CivilizationAce]

I think that SaveGameMenu.lua, the script for the Save window, could be better. In particular I want the list on the right to start filtering (or I might make it bring the matches to the top) as you type part of the filename.

Would I have to overwrite the entire SaveGameMenu.lua or is there a way to make additional Lua code run for the window? If so how please?