You are currently able to successfully edit your SkuVault Code via bulk upload by following these steps: 

1. Set up a CSV with action=edit, guid and skuvaultcode headers:

2. Navigate to Products > Bulk Upload

3. Choose your file, check Force box and skip all channels but SkuVault:

4. Click Upload 

Please note that the Code field in the product editor appears to be editable, but when you try to change it and click Update/Retry item it will revert to the old Code value. The new value will push to SkuVault but at the next sync, it will change back to match the Code value in SureDone. The only way to successfully change the Code value is to follow the above steps.