There's a novel I read years ago but I can't remember the title. Here's what I do recall, hope it rings a bell with someone....
It begins with the 2 main characters in ship called Kraftwerk II - they are chased into an asteroid field/meteor storm or some such by another larger vessel, but it turns out their pursuers were just using them for combat practice and did not really mean to destroy them.
One of the characters has been 'modified' - which means they are able to temporarily change themselves and speed up their reflexes. They grow fangs and claws as well.
Unfortunately that's about all I've got.