This is a specific case of a general principle of software design: If you have to do something more than once, abstact it. (put a string in a variable, turn a repeated block of code into a subroutine, put identical subs in multiple scripts into a library, etc.)

I don't know how extensive your script, but if it is relatively simple, I would avoid using modules and specially designed tie's when the basic tools of the language suffice. Assign the keys to variables once and then use the variables to do hash accesses. If your real code is more complex, you might look at Hash::Util or another appropriate module, or use fields with OO accessors as was already suggested.