What do I have to do to preserve a mushroom stuffing with eggs, crab and cheese as ingredients so I can freeze it for use at a later date?
But, as Catija indicates below its not clear whether you are stuffing mushrooms or whether the stuffing contains mushroom. Based on the other stuff used I am going to go ahead and guess that you are stuffing mushrooms with this, but I am going to make this and if/then answer to cover both cases.
If the stuffing contains mushrooms:
you have to decide whether it's ok for the mushroom to get mushy, then you don't have to do anything special, just make sure it's in a freezer bag and get all the air out. However, If you want your mushroom to stay firm, then don't freeze it, and wait until you get closer to the day you need to use it, then you can refrigerate it for a day or two.
I think you'll be just fine to freeze it. I might freeze the portions on a cookie sheet first before putting into a bag, it will make thawing swifter and more painless.