Filing off and filling in the
GK iconography isn't too difficult once you get into it. What might be more difficult is adding whatever details and iconography to the model you want to make the fit in with your army.
I think It will be easier to convert them to
BA than Khornish.
You will be able to hang onto some of the imperial iconography and replace the
GK ones with
BA ones.
However if you want to Khorne them up I totally say go for it. have a bit of a look at some of your favorite models and the details they use to help you get more of an idea.
I hope this helps even if just a little