Hello @panand-2
I'm not sure to have a good understanding of your business need with this question formulated a bit quikly. What I think to understand is that you would like to drive - via Pro/PROGRAM - the presence of a given component (the line stock) in a given assembly, based on a given condition - for instance, the value of a string parameter.
If you confirm this understanding, this can be done with good relations and correlated Pro/PROGRAM definition, according to the steps described in little movie attached (registered with sound for a better explanation).
Hope this helps,
Regards,
Serge
