Could the finches that evolved

bigger beaks in this study evolve

smaller beaks some day?

Yes

Explanation:

Natural selection allows for the survival of the fittest. According to natural selection, those organisms are able to live and reproduce which have better traits to adapt to an environment. Hence, in the future, if conditions become favourable for small finches then through evolution, small finches will be seen widely again. If the food sources gain become favourable for small finches, then the birds with small finches will live and reproduce more