I know about the fix where you have to add dawnguard.bsa after the update in the skyrim.editor. But is this safe to do? would my game be messed up when the actual patch from bethesada comes? Thanks in advance.

It's safe. Adding Dawnguard.bsa just makes the content in it load in the CK. I doubt the next CK update will do anything to ensure Dawnguard.bsa loads unless it, like TESV.exe, were made to automatically load BSAs by virtue of their nomenclature.