Values Default through variant table

Dear Gurus,

i have the following requirement.

I need to use the variant table in order to have output values by others input values, but i have also need to could change them.

Is there any way to change output value from variant tables?

Example:

TABLE TAB_DEFAULT (MAT= MAT , IN = IN,

OUTPUT  = $SELF.OUTPUT),

I should allow to change the value of output.

Thans a lot

Daniele