This Allegro Giocoso is the 7th of the Improvisations op.150 composed by Saint-Saens in 1916-17. The title of "improvisations" is perhaps a reference to previous "true" improvisations previously made by Saint-Saens at La Madeleine or St-Séverin, but nothing is sure.
This one is a joyful piece which can evoke some Renaissance's dance here and there.
There are two places where a registration change followed by a crescendo could make sense. But the score indicates only "Tutti" and "II" for the first 16 bars, the "I" until the end. So, I didn't change registration, thinking it is coherent with the neo-classical character of this piece.