If you want a button to remain depressed even after LabVIEW reads its value, then make sure it has a "switch" mechanism (Switch when Pressed, Switch when Released, etc.). This can be changed by right-clicking on it and selecting the mechanical action. A "latch" mechanism will reset the value after it is read.
Now if you later want to write to the button control, when your value condition is triggered, then you have several options. You can use a local variable, or a value property, or write to control by index. However, these should never be abused. Do not continually write the same value over and over in a loop, as this will hog the CPU. Also, do not allow for your code to be reading from and writing to the control at the same time, this is known as a race condition and can lead to very hard to find behaviors.
