I agree with Gregore on every count.
I've cut more than one cam prematurely and wrapped it back up to finish ripening, with success. Note that if you wrap it, you should be using special paper or foil specifically made for ripening bloomies - it breathes, but also regulates the moisture. But I would assume you could keep it in the ripening box instead. The only thing that may be a problem is that, as much as you've cut out, as it does continue to develop you may get the runny middle oozing out of the stable rind - this is why Gregore has suggested arranging it so that you put two halves together (or at least, that's why I would suggest the same thing). But with a quarter of it gone, this may be a challenge. If you have some of the ripening paper, you can cut the cheese and wrap it so that the paper helps to hold the paste in the rind.
One other comment - yes, the texture you describe sounds just right. I always have to restrain myself when the cams start to feel a bit squishy, knowing that there is still a ways to go ... but really, when to eat it is a matter of, well, taste.
I like to start on the first of a batch of cams when it gets to the point that there is still about 1/3 of the paste as a crumbly core in the middle, with soft/runny paste around it. (After making quite a few batches, I now can mostly tell, from how it feels on the outside, how far along it is on the inside.) By the time I finish eating the last of the batch, that one is generally runny all the way through. The taste changes throughout this time, and I like it all the way through the range.
