First of all, Happy New Year to all those that read this in 2019!
Now then, on to the challenge: with a POD after the Seven Years War, have Prussia be the strongest power on the continent, for as long as possible. That means that at the end of the Napoleonic Wars(if you choose to keep them as happening), Prussia chooses the right battles to fight and wins them, that it chooses allies and enemies wisely, that it gets more and more... tracts of land, citizens, etc., and eventually, as in our timeline, forms Germany with it in the driving seat of unification and unified German politics. It then goes on to build a worthy colonial empire while streamlining the premier power in Europe. Can you do it?
How about moving POD
before the 7YW and make Russia Prussian ally prior to this war? Taking into an account that for Russia this was a "cabinet war" and that, unlike Empress Elizabeth, both her heir (future Peter III) and his wife (future Catherine II) were to various degrees pro-Prussia, this does not require the ASBs to happen.
As a result the 7YW is much shorter. Prussia ends up with the relatively small losses and gets Saxony, which makes her position in Germany much stronger. If the Hapsburgs are seriously beaten then perhaps at least a part of Czechia as well. If (or rather when) Partitions of the PLC are coming, Prussia is getting a bigger chunk than in OTL (and Russia is getting a part of what Austria got in OTL: with a sustained Prussian-Russian alliance there is no need to "compensate" Austria).
If the main Russian interest is expansion at the Ottoman's cost, then it is not too much involved into the European affairs (except for European parts of the Ottoman Empire) and Prussia has pretty much a free hand in Germany either directly annexing the small principalities or creating federations along the same lines as happened later in the XIX century. Austria is marginalized: even a potential alliance with France would not protect it from Prussian-Russian alliance. Britain should be happy with (almost) anything as long as it is anti-French.
When the French Revolution starts, Prussia stays neutral/friendly (why not? the Bourbons were enemies). If by that time the Prussia-led <whatever> is spreading all the way to the Rhine then there is no fighting there (we can assume a mutually-acceptable border on the Rhine with Prussia getting something for the . As a result, scope of the Revolutionary Wars is much more narrow and limited to the Austrian Netherlands, Netherlands and Italy (perhaps Spain as well). If the Brits are failing in their attempts to expand the ant-French coalitions, then the whole thing ends up being mostly Franco-Austrian conflict on the continent and Franco-British on the seas. Prussia may even get some extra territory in Germany as a compensation (there is nobody to object in a meaningful way).
With a limited scope of the Revolutionary Wars Nappy may not get a chance but if he will (which is still a probability), scope of the fight is still limited and is not spreading into Germany. Having Nappy to die at the peak of his glory (kicking the s--t out of Austrians once more and dying soon afterwards without leaving an equally capable heir) will be helpful. Of course, ATL Nappy being a slightly lesser megalomaniac also would help: in this case Franco-British war is going forever with everybody watching with a great interest.
Prussia (and Russia) are neutral and in peace (in Europe) while France, Britain and the Hapsburgs keep wasting energy, money and people on never-ending fighting. With whatever eventual outcome expanded Prussia, which by that time controls most of Germany and is backed up by Russian Empire (which is still mostly into the "Eastern" affairs) ends up as the main continental power.
