Switch the top hotbar between the first two inventory rows.
Use Enhanced Hotbar: Previous Bar or Next Bar to choose inventory row 1 or 2 for the top hotbar. The defaults are Page Up and Page Down. Your normal hotbar controls then use items from the displayed row; the items themselves stay in their inventory positions. Opening the inventory temporarily returns the displayed bar and native inventory hotbar actions to row 1.
Enhanced Build Mode uses its own shortcuts.