Is it safe to connect a kill switch in your remote wire??

You could wire a switch into the power cord. You could plug it into a power strip with a switch and use that to control power. Most power conditioners have swtiched outlets too.
Be aware that a lot of amplifiers sound best if they are on for quite a while so are designed to be left on. When you don't input a signal to the amp they usually do not draw a lot of power at idle.