You cannot change what’s in the data table, it’s static - and that’s what Set Member attempts here. Think of it as of default values for all your needs. Fetch a struct from the DT, feed it to the actor and the actor can modify that struct internally.
And you still have the original DT struct if you ever need it.
Others have suggested to create a function that has a local variable for the struct, but i find that very clumsy.
It’s just one extra variable if you must do it this way.