Can you get more hemorrhoids even after hemorrhoidectomy?

Indeed. See below. Hemorrhoid tissue is normal, occupies the wall of the low anal canal, and helps maintain continence of stool and gas. Problems like straining or constipation cause them to become floppy and protrude or bleed. Hemorrhoidectomy removes only the most prominent tissue. If the original cause of the hemorrhoidal problem isn't improved, other hemorrhoid tissue can become symptomatic. Increase your fiber.
Usually no. After regular hemorroidectmy it is unusual to get back hemorrhoids if they recur will happen years later.