1BTC will always be 1BTC unless you take a portion of it and sells out that its value will reduce.
Apart from the value in price to reduce, the bitcoin will reduce in amount like the fraction which you have sold
A projected profit target should be reached before you sell off your bitcoin.
That is absolutely wrong. You can not set a profit target since btc price is volatile you will never know the amount of profit you will be able to make, you can only determine the amount of btc to accumulate withing a specific period of time depending on the level of your investment. For example if surely a person Target is be able to accumulate 1btc for 10 to 15years, and you achieve your set target of 1btc, you may decided to shave your BTC around 20years time, depending on when you decide to start sell off gradually. maybe by then you may have calculated the amount you have used to invest in the last couple of years during your earlier 10years when btc may be less in value compeard to the 20 or 25years time of reap, depending on when you decide to sell, then your profit can be calculated.