I think the key thought to remember RE: round two, is that the war ultimately was a challenge by Germany to the existing order of things. The world had for about a century been essentially dominated by Britain - the war was an attempt to secure continental hegemony and thus permit Germany to focus on a challenge to Britain economically, and allow for the expansion of the fleet.
However, that challenge in essence failed. The war was not the knock out blow that Germany (and everyone on all sides) expected. The advent of defensive technologies made it a brutal, protracted affair that lasted for years and nearly destroyed Germany - only to win at the last possible second simply by exhausting France to the point where holding out would make no difference.
The reason that this timeline is a CP victory timeline, rather than a stalemate one, is that even in a case of a German victory - by 1918 everyone had lost. Germany was never going to totally destroy the French army after 1915, merely exhaust her. But, Germany was able to revise most of Europe and destroy her key long term continental challenger in Russia.
So, as a British diplomat you would now be faced not with a Germany with continental hegemony, she can't force France to do anything. But, you do have a France that knows it cannot recover Alsace - not without equal sacrifice to that already given. You are lacking a Russian challenger to Germany, as the key agricultural and economic southern areas have been seperated off as de-facto German puppets. Thus Germany now stands as a de jure continental hegemon - essentially the biggest boss on the continent with no obvious challengers - but a boss without enough power to always get their way.
So, on a round two. Britain knows Germany, if left to her own devices, will now focus on eroding British global influence. As such, Britain must do her best to contain the threat - destroying it is no longer an option. Round two therefore is less a matter of 'when' and more 'if'. Should Germany attempt another go, she'll be much better positioned and the war will be very different in nature. So best be positioned as well as possible, with what limited resources you have.