Yes, it is possible and very common that auscultation findings change after nebulization with bronchodilators.

Before nebulization: Bronchoconstriction. This results in reduction in the amount of air entering thereby reducing the intensity of all breath sounds and added sounds. Only wheezes (rhonchi) are heard. Sometimes, in very severe bronchospasm, even wheezes may not be heard ("silent chest").

After nebulization: Bronchodilatation. The amount of air entering the alveoli is increased. Therefore, now all sounds increase in intensity, except wheezes. If there is a localized abnormality in a part of the lung, you may also hear abnormal breath sounds and crackles.

Hope it is clear. You may also refer to this post on mechanism of breath sound production.