My experience with heavy bent screws is that you cannot use an easy-out
on them.  As Spencer Chase mentioned, drilling a slotted screw right in
the center is impossible, anyway.  Unless the screw head is broken off,
forget easy-outs.

If, as was suggested, the screw is a large 3/8" or 1/2" machine bolt
in the leg, then that bolt is bent right at the place it threads into
the bed plate.  That means about 2-1/2" of it, or even more, is
dog-legged from having the piano leg cranked down by the piano weight.

There is only one way, In my estimation, to remove a very large bent
leg bolt like that.  Support the piano or put it on its side, and allow
the leg to circle around with the bolt as you unscrew it.  Remember, if
it can remain in its hole with the leg attached and the leg is still
able to support the piano, then it can be removed in same way.  The leg
just has to be allowed to wobble around in a circle, while you extract
the bolt.

To get hold of the bolt, if a wood screw, and the bolt just turns but
doesn't unscrew, then your threads are gone anyway, so use a pry bar and
crank the leg and bolt out of the keybed forcefully.  That rips all the
threads out of the hole.  Don't be shy.  That's the stuff pry bars are
made for.

Next, making sure all your leg bolts are identical first, clean out the
hole and stuff it with something, like slow drying, filled epoxy,
additionally filled with steel wool or anything that will make a tough
matrix.  Start threading your new hole with the new screw after you've
waxed it.  Screw it down into the new hole a little deeper than it will
normally go with the leg attached.  Then remove the screw out of the
semi-solid epoxy.  Replace the leg with the other screw hole and screw,
and then put the screw back into the epoxied hole gently.  Do not
tighten, and leave for 24 hours.  It will be fine.

The reason you replace the leg and bolt and let it dry that way, is
because the legs hole will often drift the new bolt hole over just
a bit and recenter it as it hardens.  And remember, all epoxy is
exothermic thermoplastic, meaning it gets softer when it heats up
before it gets harder.

Craig Brougher