I think that at its core, the whole release and apology is us telling the fiction that we're a "reasonable" European power that's not explicitly revolutionary in nature. All the actions with a hint of hostility against the French grows Boulanger's warhawks, as our belligerent actions feeds into their propaganda of us standing against anything France holds dear.
As is, the threat of a two-front war is very much a possibility if we don't extend any olive branches to either side. Just releasing this spy back downgrades how threatening we are perceived to the Entente and makes any post-war reality where we still exists actually bearable for them over the League.
Even then, this is literally just diplomacy and doing this should give us some leeway to do mutually beneficial "colonial" actions with the wider world without France and UK breathing on our necks.