SOLVED: Will I let the smoke out of my thing with an additional 2.4v?

No. But show a good photo of the PCB (top & bottom if possible) and perhaps it's possible to give a more accurate answer.

I can't say how valuable 5 pounds is to you.

Worst case scenario it's a 5GBP repair job :wink:
It's impossible to say what will blow if anything blows.