just go into your goals, set your loss per week to 0 and set your goal date a few years into the future. make sure you save and your ranges will be adjusted.
as far as needing fewer calories than someone who hasn't lost weight, well, you're using an average anyways if you're using an online calculator. you might run high, you might run low. but you could have already been a person who ran low to begin with. it's kinda hard to say at this point.
the best thing that you can do is pick an average set of ranges, try it out for a few weeks [or about twice that if you're just jumping your ranges up 500 cals or more] and go from there. if you maintain, then you have it. if you're gaining, then you need to eat less. if you're still losing, you need to eat more. and if you don't hit it on the first try, then bump your ranges up or down 150 cals or so and try again.