The PackRat tool allows to change various Skin parameters, e.g. Icon, Emoticon, and Sound Packs.
PackRat (developed by Tom Elmer) is available as a standalone tool. In addition, it is bundled with various skins and Icon packs, that control it via command line parameters or ini files. PackRat is compatible with Trillian 2.0 - 3.1 but it does not support Windows 98/ME.