A tool to patch total war games to enable them to save at any time in campaign. Currently supported titles are Empire, Napoleon, Shogun II, Rome II and Attila.
Download the tool. First choose your desired game. For Shogun II, Rome II and Attila choose the empire.retail.dll file present in the game's main directory. If the game is Empire choose the Empire.exe file present in the game's main directory, and it's Napoleon.exe for Napoleon. If the files are not present, then that means you don't have the latest steam version.
Tool's link: https://github.com/Overload2664/total_save_patch/releases/latest/download/total_save_patcher.exe