Once a bill is finalized and becomes law, if there's no provision for allowing exceptions under conditions, it literally takes an act of congress to change the law. A letter from the president will not do. The president cannot give you permission to break a law.

Now, in the case of California Condors the provision is there. Licensed conservationist groups and zoos are allowed to collect eggs to ensure that the eggs and chicks have a high rate of successfully growing up, they are collected and raised until they are independent and then released. this has been highly successful at increasing their numbers. Condor populations got so low because of DDT, poaching, and high chick mortality rates, not lack of suitable habitat.

Unfortunately because of the habitat issue, simply increasing their numbers by perhaps catching gravid females, releasing them when they pop, and raising the young to about a year old, would make little difference since the remaining land bearing sf garters is probably already supporting all the garters that it can, at any given time.

Well intentioned efforts to increase their numbers can hurt a species' survival in the long run, especially when there is so little remaining habitat. Introducing more snakes, or captive acquired snakes(and their genes) or offspring into such a small habitat is not a good idea for a variety of reasons. The only thing wise to do, would be to expand and restore areas adjacent to the remaining populations, closely monitor the habitat environment for issues that could threaten them, and take immediate action to correct it. Last I heard, the population is fairly stable, and only experiences ups and downs consistent with any normal fluctuations that occurs in any population of wild garter snakes. The only thing that's going to get them back to historic numbers is to restore and give them back their historic range; a very expensive and impossible thing to do.