I added an outdoor frostfree water valve to the cold water supply line by teeing it in. The supply lines is .5 inch copper pipe as is the added line and fittings. The water source is a well. The water pressure seems to have dropped a lot even when using only one faucet at a time. The added line is about 4.5 feet long. Do I have to increase the pressure at the well pump? Thank you.

The adding of 4 feet of pipe with valve would not effect pressure unless it is leaking. Check the new installation and valve to see if u are losing water.

The losing of pressure is usually a problem with pressure tank. Check to see if u have air in tank. If u get water out of air valve, u have a broken bladder and need to replace tank.

What's the PSI at the pump? What's the control box setting?
Let
S check the bladder tank.
To check, take something metal and start rapping at the bottom of the tank and work upwards. You will hear a "clunk" in the bottom half full of water. On the upper half you should hear a "clink" because the upper half should have nothing but air in it. IF the sound doesn't change or changes close to to tank top then the bladder tank must be replaced. Your air setting on the tank should be 2 pounds UNDER the cut in point in the pressure control box. If your pressure control has a 20 PSI cut in and 40 PSI cut out the tank pressure should read 18 PSI. The bladder tank setting MUST be made with the pump off and the system bled down by opening a cold water faucet after you shut the system down at the breaker box. Hope this helps and thank you for rating my reply. Tom