From Quake Wiki
AdQuedit: The Quake Workstation was created by Hicks in 1997 as his contribution to the Quake editing scene. The main purpose of the program is to supply an easy, flexible, and useable means to manipulate the many file formats that Quake has. Features include replacing textures in BSP files, editing entity lists, changing model skins, creating sprites, making MIP textures, making LMP hud textures, and extensive wad editing, and much more and all cholesterol-free!
A word of warning before using AdQuedit. All changes are saved in real-time with no undos or redos. Meaning? If you delete a file from inside a wad, BSP, MDL, PAK, etc it's gone!