In the Quotes module, there is a way to delete each line item, but there is not a way to insert a line item at a specific point in the quote. (to maintain a logical order of products).
If you want to insert a line item at a specific point, you have to insert it at the bottom, delete all the line items above it, and then re-insert all those deleted items below the new item. For long quotes with lots of line items, it is a lot of work!