If it was bought in on the planning in good time what could the German Navy have done to assist with the Schlieffen Plan, or perhaps in addition to it to secure naval objectives?
The problem with the German Navy at the start of WW1 was that they basically did not have a plan. It took them days to get going, just to organize port defenses. The "plan" was to wait for the French or UK Navy to camp off the German coast and slowly wear them down then have a decisive battle on the right day.
So the first thing they need is a planning culture that plans for various scenarios. So lets go thru the process. IMO a certainty that the UK enters a war by High German leaders means the Schlieffen Plan would be so changed as to be unrecognizable.
So, the first plan you draw up works on the assumption the UK is neutral even if a bit pro-French. It is pretty easy to see you can't send a large fleet thru the channel without a great risk of the UK entering. There are no troop ships to intercept. The land war plan calls for a war under 1 year. So what do you do with the fleet? You turn your focus to the east. You have to keep enough ships in the North Sea ports to be able to stop the French Navy from attacking. You have more ships in the Baltic. Assuming you are a senior Admiral and can't change the budgeting, you lack the forces for major land operations. But you can help. You seek a decisive battle with the Russian Navy. If they refuse to come out of port which IMO is a likely, then you bombard ports, railroad bridges near coast lines, and the like. You try to conduct raids with your limited land forces to try to distract the Russians and have them hold more troops near the coast line. Things like the Alan Islands, the Islands near Riga are tempting and lightly defended targets. If you are more aggressive, then you might do something like try to take a port (Riga or the like.) And if you want a big win and are willing to bet the farm, you would look for weaknesses near St. Petersburg. Is there somewhere that you can take that will cause Russian panic. Things like assaulting Kronshtadt will really, really get the Russian's attention. I have not done TL type research, so not sure that it is possible at start of war, but something such as bombarding the island will get the Russians attention. If you can get some land forces there or on the coastline of Russia, it might slow down things enough to help a lot in the east. Or to be fair, it might butterfly the other way.
So if this plan is run, and we assume likely butterflies. The Germans are very aggressive in the Baltic for a week or two, then they pull back the ships because of the UK threat. The Russian Navy does not offer decisive battle. There is some heavy damage to cities along the Baltic coast. And then we get to the part of the TL which is less fun. We debate do the Russians significantly change troop deployments from OTL. If the Russians hold a couple corp back thru January, then we see a series of butterflies such as helping the Ottomans, Austrians or slower transfer of German units east. Or maybe the Russians ignore the pretty obvious diversionary attacks, and it goes much like OTL,