Hi ,
If you want values to be automatically populated for a characteristic , please consider using the
"default value" in CT04.
Please check the online documentation at
http://help.sap.com/saphelp_46c/helpdata/en/ec/62ae27416a11d1896d0000e8322d00/frameset.htm
If you want the characteristic to be populated differently depending on other characteristics then
a better option would be the use of Procedures in Object Dependecy.
Please refer to the online documentation at
http://help.sap.com/saphelp_46c/helpdata/en/92/58d455417011d189ec0000e81ddfac/frameset.htm
Thanks -
Enda