Instead of copy/paste, make a building block of the text box. Select the text box (click the edge, not the inside), click Insert > Footer > Save Selection to Footer Gallery, and give it a name. To make the entry easy to find in the gallery, click Category, choose Create New Category, and make up a name that starts with A (or, better, with an underscore, which sorts to the top before anything that starts with a letter).

When you're making a landscape page, before inserting the building block, be sure to turn off the Link to Previous button in the Header & Footer Tools tab for the landscape section and for the portrait section that follows it (you'd have to do that for copy/paste, too).