Once you've opened a tin you create an apocalyptic even for that established environment inside. Might as well smoke it. And, I do find that several months is ok for blends that i only smoke every now and then.
But, if you want to keep the tobacco longer, then put it in a jar, but it is questionable whether you will geta true aging on that tobacco, some maybe you will, some maybe not.
But, if you open a tin, and then close it back up, you will never get that vacuum seal back (or even any kind of seal), unless you have special equipment.
Best practices would suggest that if you open a tin, smoke it. If you want to age a tobacco in a tin with a good seal, then leave it be. (period)
Any playing round between those lines will give you unpredictable results. But, it's not like the tobacco is going to turn to shit right away, unless the tobacco was aged for a really long time before you opened it. YMMV