Call AM_GROPRI when the field input is display only

Hello,

In some cases I need to modify the "GROPRI" field  on my sales quote's lines via SPESQH.
In order to automatically recalculate the "NETPRI" field, I understand that I need to use the following function:

Call AM_GROPRI(VALUE) From W1SQH2   

it works properly unless GROPRI field's input is set to "Display" or "Hidden".

Is there a way to update NETPRI according to GROPRI even if the field is display only ?

Thank you in advance and sorry for my poor English.