From the CBA:
The League will determine, in its discretion, a Player’s Salary Budget Charge according to the following formula, provided, however, that MLS retains discretion to lower a Player’s Salary Budget Charge in individual cases
Assuming I understand this (and other, similar passages) correctly, MLS can simply ignore a portion of a player’s or players’ salaries when calculating their cap hit. Sign Busquets for $4m yearly? MLS can say they’re lowering the budget charge to max TAM.
I’m hoping this as well. It seems like the kind of thing that would upset the balance of power between the small team owners who want restrictive salary cap rules, and large team owners who want to bring in big talent. You gotta think the LAFC and NYCFC ownership groups are asking, “and why, exactly, shouldn’t we do the same thing as Miami?”