There would be two ways of bulk editing items created through the UI:
Better (slightly less clicking the just using the UI): Use the api explorer under the developer tools. If you create the pattern you want in one item you can use the api explorer to get that metadata from that item (GET /items/{itemname} with stateDescription namespace) and then copy that metadata and paste it into the other items (PUT /items/{itemname}/metadata/{namespace})
More Dangerous 
: Editing the jasondb for items metadata directly. See the Editing the JSONDB, a last resort section of Rich’s excellent post and only attempt if you are justifiably confident in your OH backups.