If you wish to add additional custom data to asset pages you can use asset custom fields for this. Asset custom fields can be configured under Configuration\Asset Pages (scroll down to Asset Custom Fields). These fields can be filled on a per asset basis in the Edit Asset screen of individual assets.
If you wish to fill a custom field for multiple assets at a time you can do so under the Assets tab:
- Select any asset you wish to modify by using the checkbox to the left of the asset.
- Once all assets are selected click Mass Edit Assets in the left hand pane (the top one).
- In the resulting popup you can select the field you wish to edit and provide the input.