Changing based UoM

Hi Expert,

On SAP business one - item master data --> UoM group --> item code xxx1 is assigned with Packet as based UoM.

We have received stock into the system and released the Base UoM is incorrect and need to change to KEG for example.

We are finding this is not straight forward to change and only solution is to create new items.

The problem we have is that these item are retail item and item code is printed on the label already so the item code cannot change.  

Is there a way to change the base UoM when there is transaction made against the item already?