Split ROSbag to two

Hi All, I am using rosindigo on two computers. I am using a ROS bag which includes sensor data from a robot (it's the Cartographer Deutsches museum 2D dataset) used to build a map. I would like to split the bag such that I will be able to run it as if it's collected from two robots, so lets say if the bag is 2000sec long the I would like to split it to two 1000sec bags and treat it as if both halves where collected at the same time by two different robots. Would I be able to do this using rosbag filter? If so how? Would I need to fix time-stamping in the rosbag? I am a relatively new user so would be happy for pointers... Thanks