Characteristics value for user defined class type 031
How can we maintain characteristics value for user defined class type 031. Is there any specific transaction code for the same
I assume you meant user-defined data type (that's the purpose of class type 031) instead of user defined class type. Such a data type is a set multiple characteristics which are defined on the usual way.
If you're creating such a user-defined data type, a class of class type 031 is created in the background. The characteristics of the set will be assigned to this class.
To get more information on how to work with a user-defined data type, see please SAP documentation:
in section 'Introduction to User-Defined Data Types'