Design Library Parts

I'm a little unsure if this is even possible but this is mysituation.....

This there a way that I can take a standard extrusion profile andcreate a design library part out of it. So when the part is droppedinto the assembly you can change the length of the part on the fly?Also having the part that you drop be a single part file, beingthat I'm currently dropping the same part into the assembly andhaving to SaveAs on the parts to make them individual parts.

ThanksSolidworksParts And Features