unity – The way to design an upgradeable ability system?

In my recreation abilities might be leveled as much as modify base stats like decreasing cooldown by 20% and rising fired projectile depend by one. How would I architect the system so that every ability has its personal customized improve tiers for instance:

Projectile Ability Tier 1:

• Cooldown -20%
• Projectile Rely +1

Projectile Ability Tier 2:

• Cooldown -10%
• Projectile Rely +2

public summary class Ability : ScriptableObject
{
    public float Cooldown;

    public summary void Activate(Participant participant);
}

And an instance of a subclassed ability:

public class ProjectileSkill : Ability
{
    [SerializeField] Projectile _projectile;
    [SerializeField] int _projectileCount;

    public override void Activate(Participant participant)
    {
        // Instantiates variety of projectiles
    }
}

What I’ve tried:

• Storing the state within the scriptable object and updating the values. Nevertheless that is saved between periods whereas it must reset.

public void LevelUp()
{
    _projectileCount++;
}