I had that issue on about half my exhaust manifold studs. I reused everything.

I used a M7-1.0 die to refresh all the exposed threads on the studs.
I double nutted on the other end (opposite the stuck nut), then held the doubled nut while removing the stuck nut.
Once I figured what was working, I optimized things to use my little impact drivers (10.2V and 12V) to speed things along.
Red High Temp thread locker when reinstalling the studs.
Cleaned up the nuts with a tap.
Then when reinstalling things went on about 10x faster than it all came out. I used copper anti-seize when reinstalling.

Exhaust manifold to cylinder head (M7) 15 Nm (11 ft-lb). 11mm hex head M7-1.0 nuts on studs, copper plated steel nuts.

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2001 X5 3.0i, 203k miles, AT, owned since 2014