Hi Budi,
yes, sure, the logic you mention can easily be applied. Try the following dependency code, in the procedure for setting the TPREAST default:
$SET_DEFAULT($SELF, TPREAST, 10) IF
$SELF.TEMPER = 'X',
$SET_DEFAULT($SELF, TPREAST, 20) IF
$SELF.TEMPER = 'Y'.
It should hopefully work.
Thanks and regards,
Flavio