If you remove the mandatory service charge, anything you give to the service people, will have to be pooled by them. Now if you left it on your account, then anything extra you give them they would be able to keep.
If you do decide to remove it, you will be asked to fill out a form or speak to one of the Officers at the front desk and explain why you are doing this.
Don't forget - there is a 15% service charge added to all bar bills, whether it's liquor, pop, beer, wine, etc. If it comes from the bar, then there is a charge.
I may be wrong but I understood that the Hotel service charge had to be adjusted at the BEGINNING of the cruise - too late to do it at the end when you have already received your final bill. I'll check this out in a couple of weeks when I am on one of the ships.