Hello pritesh_ugrankar.   From your article:

The qr function allows for the regex to be stored in a variable so one can simply mention s/$regex_1/$regex_2/ instead of typing out the regex between the / and /.

The second part of the substitution operator ($regex_2 in your example) is a string, not a regular expression.

And therefore:

2) By saying s/$regex2/$regex1/ one can simply reverse the replacement done earlier if the need ever presents itself.

That will probably not work.