The default key for regaining control of the officer is "~", but this is not a key on non english keyboards, and there is currently (5/4/13) no key remapping in-game. To modify control mapping see the following:
1) Open the config file located in C:\Users\yourname\AppData\Roaming\Signal Ops\config.yml
2) Under the "hotkeys_game" section, find the line " f1: debug_path" and change it to " f1: select_player"
3) You can now control the main character by pressing F1 instead of ~.