Is there a way to do this…so that they can be adjusted independently. I think I have one door that is an instance of another. I'd like not to be open and the other closed. But whatever I do to the first door effects the second.
Not in this way (that I know of). The whole point of an instance is that it is a copy of the original (with scaling being an exception). If you want two differently posed items, then you will need to load two copies of it.
You should be able to copy the instance to save it's position (temporarily unparent it first if it is parented, then Edit > Copy > Copy Selected Item), then duplicate or load a second copy of your object, then Edit > Paste > Paste Pose to your second copy to move it where the instance was, then delete your instance.
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Not in this way (that I know of). The whole point of an instance is that it is a copy of the original (with scaling being an exception). If you want two differently posed items, then you will need to load two copies of it.
You should be able to copy the instance to save it's position (temporarily unparent it first if it is parented, then Edit > Copy > Copy Selected Item), then duplicate or load a second copy of your object, then Edit > Paste > Paste Pose to your second copy to move it where the instance was, then delete your instance.