You can change the season at anytime... Neighborhood view- up near the left corner is the Seasons icon. :)
You can change it back if you need. The neighborhood can be deleted and replaced -
https://www.modthesims.info/wiki.php?title=Game_Help:Reset_Neighborhoods
The location is different with the UC- C:\Program Files (x86)\Origin Games\The Sims 2 Ultimate Collection\Apartment Life\TSData\Res\UserData\Neighborhoods
Copy!- then paste it into the Neighborhoods folder in Documents (after deleting the old one).
*Forgot- Yes, Yoga does build Fitness enthusiasm. :)
http://sims.wikia.com/wiki/Fitness_(hobby)