Hi Liane, I've managed to duck the grading ritual for the past 7 or so years (they finally got me this year) for a variety of reasons - but essentially it was because I didn't want to. I was at a grade I was comfortable with and I was just fed up with gradings - I'd already had to grade from ground-up to whatever in three previous associations due to differences in "style" etc. and just could not see the point in it anymore.
I didn't so much refuse to grade point-blank as postpone until the next one, then the next, until we both forgot all about it. The main problem will be your sensei. I'm lucky in that the teachers in our association realise they are teaching adults in a voluntary activity, so the more traditional dominance issues rarely arise. My own sensei was disappointed, but you should go with what suits you (if you can).