The new store format basically locks in the store's name in the URL (this is so the link to the store remains valid even if the name changes in the future, as if the URL changes, then all old links are dead and need to be updated).
For the time being, though, you can revert to the old store format, change the store name so that its reflected in the store URL, then change back to the new store format. (Once the new format is permanent and the old format is phased out, while the store name can still be changed, it will be impossible to reflect that in the URL, so I would advise anyone considering a store name change to do it while you still can, and make it a good 'un ๐ ).
