You're simply opining. All State officials are duty bound to honor our Constitution. Montana officials rightly see that the Feds are infringing on the 2nd. This is all the 'authorization' they need.
The tenth amendment only involves matters such as state and local health regulations, police powers or issues not covered by federal law. It can do nothing in conflict with those laws. All in all it is one of the least used amendments in the development of constitutional law and appears to be essentially meaningless since the passage of the 14th. My view is that it was a sop to the slavers to mitigate their fear of fed involvement with their slaves.
View it as you like. The 10th does not stop States from challenging Federal 'law'.
State officials do swear and oath to defend the Constitution and what that document means is not left to their individual whims. George Wallace had no constitutional right to prevent Black students from attending state colleges not matter what delusion he was laboring under at the time. A delusion which passed when he recanted and for which he was forgiven. HE was man enough to admit he was wrong.
Montana has every right to challenge any fedlaw it wishes but it only has ONE legitimate venue to do so and that is through the courts. States do this all the time as was anticipated by our Founders.