Someone has a 'permanent' @voice that they set that is their default tone or manner of speaking. This can't be changed on the fly, and doesn't interact with disguise code in any way. You sound like you sound. Maybe you can change it once a week or something to allow for natural progression of accents or tonal shifts over time, but it's not something you can do willy-nilly.
Someone also has the ability to effect a 'disguise' @voice that they set and use as they please. This can be changed on the fly, but interacts with the disguise code and has a chance of 'breaking/slipping/cracking' each time you speak. Should probably scale off disguise as well as artistry, since they'd both be super relevant as implemented in SD today. Good at acting? Maybe had a vocal coach at one point? You can talk like this for hours without strain. Joebaka off the street with no 'training' in the form of UE expenditure? People are going to make you fast with your poor accent and limited range.
Comments & criticism welcome!