apply validation on existing data

[sk]

How can i apply the validation say "date btwn 2003/01/01 - 2005/01/01 on
existing data from Office Com Addin. Seems like the validation is created
but
the error checking won't take place until I put the cell editing mode(
pressing f2 )
if some knows how to press f2 from Office Com Addin this is going to be one
of
solutions.

Thanks