The trainer will cause the game to CTD if you activate the trainer in the main menu and start a new campaign. A way to get around this is the following:
1. Start the trainer 2. Run the game 3. Start a new campaign 4. Activate the trainer after the game is loaded and you are on the campaign map.
Once 1-4 is done, the trainer operates flawlessly if follow the instruction.
I've tested it with 2 fresh installs because originally I thought the crash was caused by mods I installed.
I tried your method, it works for several turns until it crash again. If I play normally (start trainer - load game) it crashes straight away. Still haven't found a solution since the OFF option on the trainer is deleted.