WGT is the 'tournament committee'.
In the Rules of Golf, Appendix I, Local Rules - Conditions of the Competition, Part C - a tournament committee is allowed to invoke the One Ball Condition.
Under that rule you would be disqualified for running out of the make/model of ball you started a round with. WGT gives you a free ball so you can complete your round rather than being disqualified.
From a practical perspective the way WGT has it set up precludes a player starting a tournament or a for wager round with a less capable ball and then switching to a higher performance ball mid-round.
As noted WGT provides a notice when you start using the last ball of a make/model and gives you the opportunity to get another sleeve at that time. If you choose to ignore the warning and assume the risk you cannot fault WGT if that does not work out for you.