Altium Component Device "Technology"
Each part I add to a schematic library gets two parameters defined: manufacturer and manufacturer part number (aka MPN). The "Description" and "Comment" fields don't necessarily specify an exact MPN.

If I want to change just one example of a part to a different MPN, I can place the part in a schematic and then just edit the manufacturer part number parameter.

If I want to add multiple of a specific MPN, I can go to the schematic library, and copy and paste to make a new component with the specific MPN. 

Having separate entries in the library for each specific MPN is actually useful, as it tends to discourage proliferating multiple similar (but not quite the same) parts in a design, which leads to better quantity price breaks, lower handling costs for purchasing and manufacturing, etc.