If you are holding a stock bought for $40 with a current price of $35 and decide to write a covered call at $39, does anything different happen than if you were to write the call at $40?
At $39, premiums will be higher than $40. With the stock price below the strike, your stock isn't likely to be called away. The only danger is if the stock price rises above $39 right? Otherwise, you simply capture more premium.