Hello I've noticed lots of people experiencing problems with MooseEdit when it comes to editing weapons or sometimes even armors which results in saves breaking, crashes and etc. and I have found a small alternative until this is fixed:
1. Pick up any random misc item or ingredient.
2. Save your game then load it on MooseEdit.
3. Select and edit the item you picked up.
4. Switch the base item to whatever weapon or armor you desire.
5. Add weapon, armor mods, or adjust the item level if you wish to do so.
6. Now you can switch the rarity to whatever you wish.
7. Save your changes and load your game!
It should work 100% without any issue i've done it several times without a single problem.
Important: You can switch the rarity even if you don't add any modifications to the weapon or armor but it won't be reflected in-game and will only show up as common. In order for it to show up correctly while doing this method you must add a mod then change the rarity.
Also once you edit the weapon and equip it don't attempt to re-edit the weapon or else you will experience crashing once again so make sure your mods and other adjustments are final!
I'm actually confused by this. How did you get it to crash? I am aware of a few ways to make it crash that I do plan on fixing, but these scenarios should be pretty rare in practice.