Altium Automatically fill Description and Comment with values from parameters
If I'm understanding you correctly, you want to be able to automatically put the manufacturer part number (from the part parameters) in the "comment" field for all schematic components. This can be done by following these steps:

1) Select all components in the schematic

The easiest way to do this is right-click on one of them, click "Find similar objects", and set "Part" to "Same". Make sure the "Select Matching" checkbox at the bottom is checked, and click "OK". This will select all objects of type "Part"

2) Set the comment field

In the "Part Comment" field, simply type "=PartNumber" (or whatever your part number parameter is called). This will automatically place the value of the "PartNumber" parameter into the "Comment" field.

3) Press Enter

This should apply the change to all of your components.

Please note this will only work if all of your components have the same part number parameter name. Otherwise you have to do it manually. There is a reason I recommend building your own libraries -- It ensures the styles (like parameter names) are all identical and you can make changes like this much more easily.