Is this method correct. Will the pid values required will be different on the fly or same. Please suggest me how to attach my quad to some thing.
Since you're trying to adjust the stability, you should make sure that your method of restraint isn't restricting the motion along that axis.
So, the preferred way to restrain a quadcopter is by connecting strings to the center of the body, above and below. Here's an example:
You could also disable the motors on one axis and run a rope under each of the propeller shafts on that axis (sideways) to simulate the lift that those motors would provide while constraining any movement.