Yes and no - there is no tool that does this fully automatic - you have to set up and tweak the chain your self, but once you're done it can be used with any input (i.e. "live").
(tl;dr: good impersonation -> pitch-shift w. formant control -> matching eq)
Like you suggest yourself in one of the comments, you have to use a mix of both a good pitch ...
For what it's worth, Adobe announced a tool (Project Voco) at Adobe Max last year that goes way beyond the typical 'voice changer' apps and EQ setups. It can literally change one voice into another with a sufficient sample of the desired voice. Scary and potentially very useful. But mostly scary (-:
Have a look at Flux IRCAM Trax vocal transformer. It can be used to changed gender and age of the voice.
Otherwise you might want to look at Symbolic Sound KYMA. This is a very expensive option however, and you need to find someone who knows how to use it well.
You can use a match EQ to read the EQ curve off of one sound recording and apply it to another. It can be used for example on a compilation album to make all the tracks sound like they were recorded in the same session by applying the EQ curve of one track to all of the other tracks.
If you use a match EQ to apply the EQ curve of a recording of Bob to a ...
One of the most common plugins used for voice transformation would be a pitch shifter. You can usually find one included in most DAW software (Logic, ProTools, GarageBand, etc). When used tastefully in small amounts, it can contribute to altering a voice while still sounding somewhat realistic. If you use GarageBand, I know there are some basic vocal presets ...