When I was prying out my oyster mushroom spawn at full colonization, I used a metal butter knife that I boiled and cooled with cold tap water.
If you stay along the edges, you should be ok. You will lose a little bit of the whitish color, but if it is fully colonized, it will make a quick recovery in your fruiting chamber.
What are you using for the substrate?
I also was "dunking" my oyster mushroom spawn to get it to fruit, so the water helped to splorp it out.
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