I would just wait to hear back from the firms and at the point you are either invited to the next stage or offered a role, speak to them about transferring to a direct TC process then, explaining you have taken on a new job which will mean you cannot now complete a VS with them.
There is no harm in asking the firms even that recruit exclusively from VS whether they can make an exception. The worse they will say is no which is no different a position than you would be if you had to decline the offer/withdraw your candidacy.
If they do have different standards for a direct TC process, you are likely to be assessed again.