Maintenance Strung too tight, how can I unhook a part?

I'm impressed/horrified that after a few years the strings are still that tight Dream Valley is infamous for absurdly tight stringing.
Honesly I would just cut and restring the poor doll. The elastics have probably lost their give, and cords that tight can warp or crack the resin so you can do no wrong.

 

Do you have a wooden chopstick or a bamboo skewer? Something long, thin, and wood? If so, you can pull the wing shoulder joint out just enough to get that chopstick in there, put it through the elastic loop, and that'll keep it from going back in while you do the unhooking. I wouldn't recommend doing this with a plastic or metal item, as they could damage the resin.

I use this technique for changing hands and feet, but it works for anything that attaches at a joint like that.

 

If you have a thin ribbon, I would recommend pulling the elastic enough to create a loop, slip the ribbon in, and use that to hold as you remove the wings. It helps a lot to have that so it doesn't shoot back in and really helps for parts like that.