Need help on Arduino as ISP If I use an Arduino board to bootload a new chip, is it still possible to use the microcontroller on the board for another project, or it will only be for bootloading new chips.
There are more ways to flash a bootloader to new AVR chip. To which you refer? If you replace the chip on Uno to burn a bootloader to it with a programmer, then it is very unclear what you are asking, because the original chip is not involved in this process.

If you ask about ArduinoISP sketch, then simply it is a sketch. You upload it as any other sketch and replace it with any other sketch.