Basically an example of what @Jacky mentioned in their answer.
Currently dealing with PostProsessing settings in BP’s is not very nice. (It gets very messy very fast.)
As there is no way to set individual properties in BP (For whatever reason)
You will need to get a ref to the volume, break the settings, pass all settings other than those you want to change to a set members node, (so those values remain the same) and then finally set any values you want that are different on the “Set Members” Node.
It’s incredibly ugly. I ended up writing a BP function in C++ that blended two volumes as it was less of a pain to do.
(NOTE: the error on the Set members node is because i got lazy and didn’t join all the Nodes. 
)
