Hello.
I am trying to create a video along a proposed railway alignment over the acquired point cloud data using the "Recorder" feature. As I go along the alignment and keep adding "Camera" locations, it is becoming difficult to keep the height and the orientation angle of the multiple cameras same. I need to keep it same all through the video to ensure a smooth video fixed at the same height and orientation. Is there any procedure to create such a camera path with fixed camera orientation, like a 3D CAD line and import it as camera path?

You unfortunately cannot import a 3D CAD line.
However, you can click the "Reset view" button in the top left corner, giving you a perfect bird's eye view. After that just click and hold the scroll wheel, and move around. This way you will stay at the same height at all times.
You can also try using the "Free flight" mode (fourth option to the right from the "Reset view" button), which mimics the drone's flight. You use the A, S, D, and W keys to move around, always staying at the same height.