Hi I am using a Force search to set a variable waypoint using get_actual_tcp-pose() but I then need to modify this waypoint in the Y axis to stop the head 200mm back from the actual tcp position from the search. Can I do this using trans_pose or is there any easier way?

Do you want to move in the tool frame of reference or the base frame?  Pose_trans uses the first pose you give as the frame of reference so tool for instance, pose_add uses the base frame of reference. Remember that position is given in meters and rotation in radians. 

I want to be able to adjust the tool position so that once it has found the edge of an object from a force search I can return to the same position but be 200 mm back from the recorded search position, I tried to use Pos_trans. With but had error message saying that it could not reach that position. After my force search I tried to record the tcp position into a variable then used tried to Pos_trans this variable with another with axis p(0,0.200,0,0,0,0) to try and achieve a new variable with this modified position with the Y axis back 200mm?

So you may not be able to reach the new point, you can use 

pose_trans(Tool, p[0,0.2,0,0,0,0]) where Tool is chosen from the pose drop down in the formula builder screen, not typed in. When it generates the script it returns get_actual_tcp_pose() in place of Tool. 

Make sure you really want to move in the y-axis of the Tool, direction opposite the Tool I/O port. Assuming you have not rotated the TCP around any axes in the settings. 

What is the pose that that is returned when you caclculate the new  waypoint?