Make Material Copy
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(Material Editor): Compact (Make Material Copy)

Compact Material Editor menu bar Material menu Make Material Copy

Make Material Copy "cools" the current hot sample slot by copying the material to itself.

The sample slot is no longer hot, but the material retains its properties and name. You can adjust the material without affecting it in the scene. Once you've got what you want, you can click Put Material to Scene to update the material in the scene and change the sample slot to hot again.