The easiest thing would be use automatic selection to slowly and carefully select all the line art, and then copy it to a separate layer. Then you can clear the layer that has the parchment texture and import it again. So then you’d wind up with 4 layers, ocean, terrain, line art, parchment. level 2
On the Layers panel, click Edit All Layers. To select an object: Do one of the following: With the Move Tool selected, click an object or group on the page to select it. On the Layers panel, click an object entry. Select>Select Next/Previous will select objects sequentially within the same layer (or group) as the initially selected object.