Defining a parameter that can only be read on the screen and set in the variant?

Hi

Is it possible to define a parameter that can only be read (read only) but the value can be set in the variant.

For example.

SELECTION-SCREEN BEGIN OF BLOCK 1 WITH FRAME TITLE text-005.

PARAMETERS:   directory(40) type c OBLIGATORY.

PARAMETERS:   nr type i OBLIGATORY.

SELECTION-SCREEN END OF BLOCK 1.

The parameter "directory" should be set only in the variant and the value should be "read only" on the screen after selection of the variant.

Is possible to implement this? If yes, how?