Marvel changes the course of comics history with a single letter

We've known for a while that the new Thor is going to be a woman, but how does that work? The hammer itself specifies the gender of the hero that wields it, so something has to change, right?

Marvel is doing a whole lot with a single letter. Here's a preview of the issue:

Now, there is precedence here. Thor's gender was changed in the comics, and Wonder Woman was found worthy when she picked up the hammer but quickly rejected the power. This is different though. A female character is accepting the mantle of Thor, and the inscription itself has changed to reflect this fact.