This is one of the uses for Design Pattern: Human Readable Names in Messages though I would choose either a MAP or a JASON file over XML and XSLT. If you must use XML, at least use XPATH. XSLT is really hard to use for something like this.
Another alternative is one can load a .properties file (it’s basically an .ini file) that you can load into your Rules into a Map<String, String> with a couple of lines of code. But it wouldn’t work with Scripts because you can’t pass the Map to the Script as an argument meaning you would have to load it each time the Script runs. If you have to do that you may as well save a line of code and use the transform Action.
Of course, unbound Items are also an option like job recommends.