We are starting second plantings soon and are already planning over winter action. Pat wants to spread the garden with mushroom manure in November and I had planned to over winter some things including the onion family. My understanding is that mushroom manure smothers all...so is it safe to do--provided I clearly mark row areas so they aren't tilled in the Spring?

Apologies, but I didn't read all the other "manure" threads...

Actually it is just spent compost that was used to grow mushrooms, and then sterilized, or sterilized first.
Anyhow, it seems fine to use as a soil amendment, although it is a little alkaline.

I dont see no reason not to top dress with it, never seen it hurt anything at all, maybe someone else can add more.

Whether that mushroom "manure" would smother what is growing in your garden or not depends on how thick you plunk it down. If you put a couple of feet worth then it will smother everything, but an inch, carefully applied, will not.