I believe for last set/get blocks you can just use: get or set and change call mode in the inspector to instance.
Like this (GLOBALS is obviously singleton here):
You can easily search for those. Just right click on empty and type "set(" or "get(" and you'll find them.
Full codes in search are: Set(String, Var) & Get(String).
You don't have to use singleton to access and change variables, you can do it in any scene script that is present on live (remote) main scene (use real path from remote) or you can preload-instantiate scene that is not there yet.
You can also use "propagate_call()" in search: Propagate Call(String, Array, Bool), to start/call any remote function but it has to be on a script attached to scene. As far as I know for now you can't call function from alone script (not attached to some scene).