You could create an isAltPressed? Boolean variable. When pressed the input Alt, set it to true and on released set it to false. Then for your camera rotation just do an if statement (branch) with the isAltPressed? Boolean as the condition. 
You could create an isAltPressed? Boolean variable. When pressed the input Alt, set it to true and on released set it to false. Then for your camera rotation just do an if statement (branch) with the isAltPressed? Boolean as the condition.