I would first try to just ask the firm you have been first offered VS from whether you could be moved to another scheme. There's a good chance they might, in which case your issue will be resolved, in that there will be no conflict even if
Paul, Weiss makes you an offer. In case the firm responds that thy cannot do so at the moment, I would accept the current offer and then see what you can do after you get a response from
Paul, Weiss. It is quite possible that even if the other firm cannot accommodate a change of date now, by the time of your scheme people will drop out/request change of date, in which case you will be able to switch then. Worst case scenario, where there is no flexibility on either side, you can simply withdraw from the scheme of the firm you are less interested in and try to negotiate a change to a direct TC assessment with them.