Well, I guess, just hope you get good service. I bet you will, and then it won't be an issue. You can cancel any future cruises, and it turned out just being upset over something that turned out to be a non-issue on one cruise.
If you don't get good cruises, how much are we talking about? Even if you think service was only half good, what's that? $50? Given all the changes that they can make to a cruise without giving you notice, this seems pretty minor to me.
Finally, I really don't understand the 9-day point. What if they had changed the tipping policy today? That it changed a year ago doesn't really seem relevant. If they had changed it today, you'd still be in the same situation.
The reality is this: A cruise line can make changes that you don't like at any time, including 9 days before your cruise, or even one day before the cruise. That's the gig. If it's a significant change, you can usually talk your way into a free cancellation. I think one can debate whether this is a significant change. I view it as up there with a change in the hours of the pool, but either way I think
DCL is usually pretty good about these and will let you out if you press it. If you're not prepared for the fact that changes can happen in cruising that can cause you to want to cancel, and nothing less than reimbursement of your ancillary expenses in such event will be palatable to you, you'll always have potential issues. But even so, have you tried to get them to pay for your expenses? Why not have your
travel agent call them and see, or if you booked yourself, just give them a call. Tell them your concern, ask them to cancel you, and ask for reimbursement of your reasonable expenses and see what they say. Or perhaps they would even change the tipping policy for you in a way that doesn't require you to go to GS.