New freeware: RegXchg

This utility will allow you to switch specified registry value between two given data, for example changing hidden files' showing state (xchg_hidden.cmd inside distribution package). As of yet, it supports DWORD values only; it's meant to alternate *yes/no* system settings. To get detailed info on how to use it, download it, unpack to %windir%\System32 and call (from elevated command prompt) with /? switch.