The main water shut off valve nut inside the house is cracked and needs to be replaced. It has a turn knob like your outside water hose has. To change the nut can you turn the water shut off value off and take the knob off and replace the nut or do you have to turn the water off from outside?

The main water shut off valve nut inside the house is cracked and needs to be replaced. It has a turn knob like your outside water hose has. To change the nut can you turn the water shut off value off and take the knob off and replace the nut or do you have to turn the water off from outside?

I take it you're referring to the bonnet packing nut on the stem, (see image).
If you have a replacement nut then simply turn the valve off. Remove the handle and nut and replace the nut. A word of caution. Do not overtighten the packing nut. With the nut on loosely turn the water on. The nut will begain to leak. Snug the nut up until the leak quits. STOP !! It's tight enough! Good luck and thanks for rating my reply. Tom Tom