When you book a site (Club or Private) you are entering a contract. Generally most people accept the companies terms and conditions, and that's fine, provided they suit your needs or wishes.
But contracts are an agreement between parties, and there is nothing wrong with suggesting some of your own amendments to suit specific needs. BUT you must also bear in mind it is an agreement and all parties must agree to the document before the contract is confirmed.
In fairness most companies are not likely to accede to variations, as they would need to seek advice from their legal teams, and that would not be popular. But in difficult times perhaps they might be prepared to consider minor variations if it increases bookings and therefore income.
One you have agreed to a contract you cannot then change the definitions of any T&C's unless they can be shown to be unfair, or all parties mutually agree to the changes.