Comments - Phalacrocorax

As I've written below: try to run OpenTexMod.exe and AssassinsCreedIIGame.exe with Administrator's privilege. An attached manual in screenshots worked for me (I've got the Uplay version and W10). In OTM you need to only add AssassinsCreedIIGame.exe and tick "Use global hook", then launch a game normally (still with adm privileges).

Have you tried to run OpenTexMod and AssassinsCreedIIGame.exe as Administrator? For me it helped for issues with detecting launched game in OTM.