Yes and no.
You can override the existing voice sets with custom-made ones of your own (or other ones available online, on the Vault, or elsewhere.)
However, this works only to override existing sets. So you and everyone else who chose your voice set will have the new voice. Due to some complications with the way Bioware handled voice sets, adding additional PC voice sets to the collection is terminally non-trivial.
Edit: Apparently with Custom Content Guide #3, there are new ways to do this. However, they require that a new soundset.2da be placed in your override folder, along with the .wavs that you're using. While this would give you the voices, I'm not sure how it would behave with Layonara's hak paks - and, of course, anyone who didn't have the override, even if they played together nicely, wouldn't hear your voice.