Can I repack toilet supply valve?
I have repacked these valves many times using Teflon rope. I have even done it with Teflon tape but the rope is easier and last longer. Turn off the main supply and bleed the pressure remove the gland nut and back the assembly out (good time to inspect the seat and replace if deformed), I have a kit of seals I purchased years ago with 4 or 5 different sized seats, some shaft packing (Teflon rope) and some new rubber seals a good idea for any home owner to have a kit like this to repair faucets under 10$ and just add as you use up and save over a replacement.  I will usually wrap the shaft with at least 3 full turns and more if the shaft is in bad shape put the assembly back together and tighten the gland nut turn the water back on bleed any air out of the line and check for leaks. I do not back seat (fully force the valve open as this is hard on the packing) I learned this with SCUBA diving where you open the valve fully then close it 1/2 to 1 turn to extend the packing life.