Changing to a heavier or lighter line does not change the action of a rod. Rod action is an inherent physical property of the rod.
It may change how you perceive the action. Same as of you put a line on the rod and change the amount of line outside the rod tip.
If put a 5wt line on a 5wt rod, strip of 30 ft of line and cast it, the road will bend and unbend (load/unload) a certain amount. Strip off 35ft and it will bend more. Only 25 ft it will bend less.
Now put a 6wt line on the same rod. You will find that 25 ft of a 6wt will feel about the same as 30 ft of the 5 wt line. The action has not changed. You have just used a shorter length of a heavier line to provide the same load as a longer length of a lighter line.
Changing lines doesn't change a rod or make it better or worse. It may make it better or worse for you though, which is good enough reason to experiment.