Yes, you can enter a custom calorie target. Go to the 'Weight Goal" tab then go to 'Calorie Balance' tab then click on 'Customize Calories You Can Eat'.
I created my own spreadsheet using the Harris-Benedict equation for RMR. I have it set up to track the variance between my projected and actual weight loss. While the day to day variance can be as high as 1.5 lbs. the total timelime for my tracking (4 weeks of data) is only off by .2 lbs. My average daily loss projection is 0.318 lbs. and my average actual daily loss is 0.321 lbs.
The Harris-Benedict equation works well for me even though it's not taking into account lean/mass percentages. I also use the sedentary setting and then use FitDay activity log to come up with my additional burned calories.
Hope this helps.