The MCU hammer doesn't have the inscription.
I haven't found an indication that there is a physical inscription on this version of the hammer at all! We see Odin speak the enchantment over the hammer in the scene where Thor is banished, but we don't see any inscription or writing/lettering.
Edit: Evidence for this provided in the answer to this question, with thanks to Valorum: Does the MCU version of Mjolnir carry the "Whosoever holds this hammer..." inscription?
If the inscription is there, it could probably be changed.
If the comics are any indication, even if such an enchantment/inscription WAS on the hammer during Hela's time wielding it, it is changeable: when the female Thor took up the hammer, the inscription changed, replacing "he" with "she". No one had to make the change, it changed of its own accord. It's not a stretch to think that Odin would be powerful enough to have the inscription added as he enchanted it, or to alter it if one already existed.
The hammer wasn't made specifically for Thor.
There are several variations of Mjolnir's origin in the comics, but of the ones I've found, none of them actually have the hammer being made specifically for Thor at all. In the base mythological origin, it was simply created as a gift to the gods, and it turned out only Thor was strong enough to wield it one handed (due to the short handle). In another, it is forged from the heart of a dying star. In still another, it is made by trapping a giant sentient space storm...thing...in a lump of Uru, which is forgotten for a long time before Thor finally appears and is able to wield it. In all of these cases, the hammer was made for other reasons, and happened to find its way into Thor's hands to become his signature weapon.