Text to Speech - Change Pronunciation?

I know that its possible to change the TTS pronunciation of a specific word within an authored program using a lexicon, but has anyone developed an  editor that modifies the pronunciation of a word for all apps and the OS itself by modifying the user TTS lexicon? The non-MS sapi5 voices such as Ivona and CereProc have their own TTS pronunciation editors that take PLS files as input, but I'm not that keen about writing my own for the MS-voices if someone has already done so.