Is there a procedure to whiten a traumatized tooth from the inside?

It is only possible to whiten a tooth internally following root canal treatment.  There is a risk of external resorbtion anytime internal bleaching is done.  It often makes more sense to utilize a veneer or bonding to cover the discoloration.

No, what you're referring to is "internal bleaching" which is oftentimes done on teeth that have had root canals and the tooth has turned dark because of the trauma that cause the tooth to need a rood canal (i.e. deep cavity, blow to the tooth), etc.Please understand that bleaching works very well on enamel, the hard protective outer part of the tooth.  However, it doesn't not work as well or predictably on the inner part of the tooth, the dentin, which is more organic and darker in color anyway.  If the tooth is darker near the gum line, then the dentin is the inner part that is most likely discoloring your tooth. Any type of bleaching, internal or external, may be ineffective there.However, it's worth a try to use a repeated external bleaching with trays.  Eventually the bleach will permeate deeper into your tooth, and should lighten it somewhat.  Remember that if you use tray bleaching, and only trying to whiten one tooth, don't put the whitening gel in the tray for all the teeth.  If you did that, all your teeth would whiten, but the darker tooth would be lighter, but still behind your other teeth in regards to the lightness.Regarding veneers, they do not "damage" the tooth and although you don't "want" a veneer and any tooth "preparation" (i.e. drilling), that may be the most conservative and predictable way of addressing your tooth discoloration. 

You can bleach a tooth from the inside but it does require that the tooth no longer be alive. The internal of a tooth can only be safely accessed in a tooth that has had a root canal. You can try external bleaching and leaving the bleach on the single tooth for longer or using a more powerful concentration of bleach on that tooth to try and lighten it more.