Need to change data type from character to number for EFF

Hi

We have a requirement to enforce decimal precision for an EFF in Problem Report in Quality Management. However the data type is of type "Character". We understand that the data type should be of type "Number". In order to achieve this we need to remove this EFF and create a new EFF (with "Number"). However the values captured in this EFF for existing Problem Reports will be lost. Is there a solution to retain the EFF values for already created Problem Reports while creating a new EFF

thanks