Gadget settings are applied only to utterances that are not loaded when they are saved.

For speech rate, it would probably not be to hard to change this, either by setting the rate for all utterances on save or store the rate to a variable and set it for each utterance when it starts playing.

For voice, utterances would need to be reloaded on change. This is probably easiest done by just throwing away all the old utterances, causing them to be reloaded when they are played (again).