you say the exciter is usually applied to a whole mix, from what i read it is applied to just the vocals. So this would be out of the ordinary to apply just to vocals?
If you have all the multitrack files available, then it ought to be possible to manipulate what you've got to get an acceptable sound without having to resort to overall excitation - it's more generally used to 'liven up' a mix that's already done, and that you
don't have the individual files for.
So in theory you shouldn't need to apply it at all - but people still do use it to give an overall 'sheen' to the sound, and that's what is easy to overdo. There's nothing particularly
wrong with just applying it to a single track, but in general you wouldn't do this. But in the end it simply comes down to whether what you did works or not, really - and there aren't any specific rules about this, except for one; Use your ears!