You can easily bulk add products to a Linesheet or a Custom List directly through your "Browse Products" page. You have the ability to "select all" or apply specific filters to your product search.
First, you will want to select one product box located at the top left hand corner. From there, click "Select All that meet search & filter criteria", and then "Actions".
The next prompt will be to 'add to top' or 'add to bottom' - this is helpful in merchandising your linesheets/ custom lists. You'll then have the ability to select to add those products to either a new or an existing Linesheet or Custom List.