Congress is almost completely red. So of course they are going to do whatever Trump wants them to do and pump whatever laws and regulations (or lack thereof) that he wants in place. Includes replacing SEC head if they find some ancient provision that lets them get away with it.
Yes, Congress can change the law I suppose--and Trump could simply ignore the law, although I suspect this isn't a hill he's going to want to die on right now.
The US Congress is nearly 50/50, with the Senate now having a slight majority for Republicans. The House still might be majority Democrat when all of the votes are counted in the coming weeks.