It *is* possible, but it's probably not a good idea - most operating systems assume external drives and storage devices to be of a specific type of file system, and setting such a device to something other than that specific type of file system could prevent that device from being read from such operating systems and basically render the device useless (or atleast cause the device to require reformatting, thus, losing data) - it's basically possible to convert any device from one file system to another if you know what you're doing, but there's rarely a decent reason to do so. If you really want to do so, just search for some decent partitioning software that supports both FAT/FAT32 and NTFS - most will do so, and are able to convert between them.
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