It might be, but to do so is so far beyond our understanding of genetics and biochemistry as to lie in the realm of science fiction rather than science. Our current knowledge of genetic engineering allows very limited "copying" of traits from one organism and transplanting them into another. We know nothing about creating new original structures from raw genetic codes.
The principal problem is that all Earth life requires liquid water within the organism. To keep the water from vaporizing and boiling away, the organism must be as gas-tight as a spaceship. If shell or bone or coral or something were used to seal the organism off completely, there would be no way for matter to enter or leave the organism: it couldn't eat or excrete. You're stuck between the need to seal yourself off from the environment and the need to exchange matter with the environment. Current Earthly lifeforms use selective transport across cell membranes to take the "good" things from the environment and keep the dangerous stuff outside -- however, these are very flimsy structures, and couldn't stand up to vacuum. A completely new way to take in nutrients is required -- perhaps the equivalent of an airlock. We have nothing to copy or borrow from to achieve this.
An even tougher problem is that outer space is, by definition, empty. The fundmanetal processes of life are growth, self-repair, and reproduction. All of these require the organism to acquire nutrients and collect matter. There is so little matter in outer space that this would be impossible. Now, if you include the surfaces of planets, asteroids, comets, etcetera in your definition of "outer space", life might have a chance of collecting the matter it needs. But having plants and animals floating out between the planets is probably impossible.
To summarize, the problem with modifying Earth life for outer space is that there are no Earthly organisms which have any system to protect them from vacuum while still allowing matter input/output, and our genetic engineering ability cannot (now, and for a long time to come) design completely new structures. Even if this problem is solved, life could only be possible near sources of matter like planets and asteroids.
Try the Evolution links in the MadSci Library for more information on Evolution.