Yes, but That essentially will make it longer, but not taller, unless, or course, you mean to use the 2nd castle to make the 1st one taller, which is not a bad idea at all, but that may lead to big blank wall syndrome and arkwardlrepeditive interiors.
If you did use the 2nd to increase the height of the 1st, do you have any pics? I would love to see that!