Yes, this is not a problem, as these are so-called "finishing products" that are applied after the Thymuskin Serum has been applied.
However, please ensure that you wash your hair before applying Thymuskin Serum again. As there are residues of mousse and hairspray on the scalp, there is a risk of massaging these into the scalp together with the Thymuskin Serum, which can lead to skin irritation.