You're really not explaining yourself- WHEN are you using V2 in place of VREF 30?
VREF 30 is only relevant when AT flap 30. It is 1.3VS at flap 30.
V2 will change with a number of Take Off parameters. It will be different for a flaps 5 TO then for a flaps 15.
They are used for different things at different times- HOW do you use one as the other?