In AIM, you can search for the material, change its properties or create a new material and then export it to the same imported library or to a new library or default AIM material library. Please check out Physics - Material Assignment - Exporting material section in help document. If you are exporting the material, it will get overwritten if the material already exists in that library.
You can check the location of the material library by clicking "Library" option as shown below.
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