Well, language is completely made up, and therefore, yes we absolutely can decide how it works. Yes, we absolutely can redefine, or rather in this case, expand terms to encompass more than their original meaning as we grow and evolve.
It's personally distasteful to you for some reason. I understand, but that doesn't mean that language is, or indeed ever was, set in stone.
I disagree that you can decide how it works unless you give up language as a tool of communication with others and simply use it as a means of expressing only yourself to yourself.
It should be offensive to no one to refer in biological terms when it comes to physical attributes and morphology, and rebutting scientific baselines for the sake of feeling is like catering to the people who think that Adam hung out with dinosaurs and the world is only 6,000 years old.
Transgender people are special. They have a particular biological forum and the urges of another gender, but we are more than urges and biology so they are also amorphous creatures of spirit. We are more than our body and our sexual urges or even our inclinations. We are free spirits capable of endless thought so none of us truly can be held down by a concept of gender, either. We are more than biology, gender, or sexual preference.
We are individuals.
Individuals are any number of things. They are biologically a woman who lives life from the perspective of a male gender, but also likes to drink mead and sing songs with his friends. Does Krem read? Does Krem like poetry? Does Krem have a horse or like pets?
Krem is or should be more than a transman. That would make Krem an amazing character and I'm sorry we don't have that opportunity to see that like we did with Sten and his paintings and the kitten.