While federal laws do not change on a rapid basis, especially these days with the never ending posturing and ineptness of the branch, executive "policy" can change very quickly. Policy differs from law in that it is set within the administration itself and not by Congress. For example, Congress may outlaw marijuana possession and cultivation but the Executive Branch (President) can refuse to enforce the law.
Certain laws were heavily enforced during the Obama administration but others were loosely enforced. Towards the end the Obama policy on marijuana was to more or less leave state compliant cultivators alone so long as kids or gangs were not involved and there was no guns. But the administration also expanded the asset forefeutre department. What will the Trump Administration do differently?
One thing that seems certain is that with the appointment of Senator Sessions for Attorney General, marijuana users and growers will have great reason to be afraid. He has a well documented history slamming medicinal marijuana. So, it seems certain that in California where the voters made recreational marijuana useage legal, it may also result in more federal prosecutions. But what is also certain is that with Trump there is no certainty. We shall see.