looks like u need to cut the pvc pipe below the elbow to able to rotate the connector to the nipple.
i assuming its reducing nipple? 1" to 3/4".
need buy pvc soket connector to join back the cut pipe.. and pvc glue too.. and white tape..

u can maintain the rest, but to take out the nipple joint, u have to turn the pipe.. its threaded nipple joint. that's y need to cut 1 part of pipe and after replaced nipple joint, need to join back the cut part.

Is not expensive to change the entire length from on/off valve to the nipple ... about 10 - 15 bucks for materials.

no cant do.
its 1 way thread, u turn clockwise will tighten to the valve head, anti clockwise will tighten to the pvc socket.
anyway do, still need to cut the pvc pipe to 'free' the nipple.

item is cheap actually, but the 'cost' is 'perjalanan' and time of the plumber.

Water pipe have std size
U need to make sure the size of the pvc and alao the nipple size
If not sure can bring the assembly (after cut out) to hardware/pipe shop.
They will help u getting the right part.

Water is not dangerous like electric.. like my FIL said..
After all... Will get wet only... Haha 😂