If the season hasn’t begun yet, can I go mountain skiing at the resorts without a Mountain Pass?

Yes, you will be able to go mountain skiing at the ski resorts without having a Mountain Pass, as long as the season hasn't begun. But it is important to remember that, although the resorts aren’t open to the public, the specific rules and recommendations for this must be followed.
It is prohibited to bring dogs onto the slopes
When ascending, the user must go up the right-hand side of the slope in single file.
It is important that those engaged in the sport are aware of snowplows, other machines and resort vehicles that are working to prepare the slopes. The utmost caution and respect is required.