Del is correct. The only reason the Hi-Res pack is an external download is to reduce the size of the initial installer for people freshly downloading the game who don't want it. Leaving it installed has no effect at all except however MB of hard disk space they take up if you switch the texture size to something other than 1024.
Conversely (for anyone else reading this topic), the 1024 option will display in 512 quality unless you install the HiRes package.