Does DW say anything about the MC having free reign to change the rules to better suit the game they want to run if they want and make the game their own?
Nes. Yo. Naybe.
The question cannot be directly answered with "yes" or "no" because it is in conflict with the fundamental assumptions and structure. It is
somewhat like asking if the rules of chess say anything about the referee granting the players the ability to bring fairy chess pieces instead of standard ones. Or, just read what
@Neonchameleon wrote. DW is a toolbox; D&D an instruction manual. Trying to
reforge your wrenches isn't going to make your toolbox more useful, especially if you're doing it in an unfocused, pure-exploratory manner.
DW, like pretty much all PbtA games, has been tested
extremely rigorously. That doesn't mean it's perfect (it's
definitely not! I have had issues!), but the type of absolute "blow EVERYTHING up and do ANYTHING you want!!!" freedom you and others speak of just doesn't...work. If you try to do that, you are
nearly guaranteed to have a Bad Time. You are
nearly guaranteed to feel frustrated and denied, like you're trying to swim through the La Brea tar pits. Not to torture a metaphor, but if you constantly re-forge your own wrenches and screwdrivers, you're going to have a rough go of trying to disassemble anything that uses mm/fractional-inch bolts or Phillips-head screws...and the vast majority of the time you're not going to get that much
use out of your custom-built pentagonal-edge wrench that you made so you could open fire hydrants when you wanted to.
But there are two very critical elements here that are the
other reason why this question is essentially impossible to answer. First, the game specifically gives you both examples and advice on how to construct your own moves. The first like two thirds of the Advanced Delving section of the GM rules is all about this (and Classes, and similar). So...if you find you need a move and there isn't one for the purpose you want...just...
make one? I've done it many times and I'm really not that experienced as a designer. (In fact, I can say with just a little bit of pride that I've only had to truly
rewrite two moves, one of which was for a magic item, the other for a Compendium Class feature.) People put out variant playbooks (=classes) all the time, there's
scads of the things. Heck, I even got one for the party Bard that was a full
booklet worth of Rogue-aligned playbooks, at least half a dozen different takes on what it means to be "a Rogue" (e.g. the gentleperson-thief, the brutal enforcer, the silent assassin, etc.)
Second...the
last third of the Advanced Delving section specifically discusses
why changing the guts and bones of Dungeon World is risky and likely to cause issues, but doesn't tell you that you
cannot do that. This is the start of that section (note its subheading is "The GM" because the previous subheadings were things like "Moves" and "Classes"):
The GM
Changing the GM’s side of the rules is an entirely different beast from writing custom player moves. Writing GM moves is the easy part. Since a GM move is just a statement of something that fictionally happens, feel free to write new ones as you please. Most of the time you’ll find they’re just specific cases of one of the moves already established, but occasionally you’ll come across something new. Just keep in mind the spectrum of hard to soft moves, your principles, and your agenda, and you’ll be fine.
Changing the GM’s agenda or principles is one of the biggest changes you can make to the game. Changing these areas will likely require changes throughout the rest of the game, plus playtesting to nail it all down.
Many--indeed, nearly all--of the "change the rules to better suit" examples you could come up with are going to fall under what that first paragraph describes. Few of the mechanics that are binding on the GM are really going to be that offensive...unless you're genuinely committed to the need to just outright lie to your players about the world or the like.
E.g., I cannot fathom a reason why a GM would ever
want to disobey the instruction to give an interesting and useful piece of information as a result of a 10+ Spout Lore roll, aka the DW equivalent of a Knowledge check. The whole
point of a character getting a high result on a Knowledge check is that they will get information that is useful to them. To disobey that instruction
is, in any non-contrived case, going to mean you're deceiving them simply because you
want to deceive them. Much the same applies to Discern Realities (equivalent of Perception); the questions are restricted in part so that the GM isn't getting instantly asked the deep fundamental secrets, and separately, the player's actual actions and descriptions shape the kinds of answers they get. There is, for example, an NPC my party has met and knows reasonably well, which they don't know is actually a black dragon in disguise. They have heard
many suspicious things about the fake identity the dragon hides behind, but they have never put two and two together yet. I haven't
lied to them at any point; I have very rarely even needed a lie of omission, which is acceptable (albeit maybe skirting the boundaries) per the rules.
So...in one sense, the rules don't just allow, they explicitly
instruct you to create rules. All the time, even! Monster moves, location moves, general moves, class moves, the works. But in another sense, they explain why the game's structure is what it is. That ripping out something as important as any of the Principles or (especially) the Agendas would mean you were, functionally,
designing your own new PbtA game, with all of the effort that such a thing entails. Some discussion is given of which Principles are utterly essential to the function of DW (more or less, "these are what facilitate PbtA play; break these and the game probably won't work anymore, or will run aground
a LOT"), which are essential to the setting-concept its creators intended (and thus very signfiicant to the
feel of the game, but not to whether it will
function per se), and which are important primarily because they're best-practices (such as "Draw Maps, Leave Blanks"). Finally, they also list one commonly-added additional principle ("Test their Bonds"), to show that the list needn't be only
shortened, it's possible to add others.
If you
really care enough, I can go over some of the "house rules" I've applied to DW. None of them change
that much, but they are part of making an Arabian Nights-themed experience rather than the particular kinda-gritty, kinda-mercenary flavor the original creators were aiming for.
