Can EOs be undone by other presidents? Can Obama's eventual replace erase all of Obama's EOs?
Yep. Hank and Slingshot are correct. Imports are the only place an EO could do "real" damage. Exports are more of an industry thing, and aren't that much of a deal for the consumer firearms market. Good luck banning Boeing, Sikorsky or LockMart from exporting. Barrett, Remington, etc are mostly selling either fairly neutered weapons or to foreign police/military. They can't tax exports. Ban, yes. Tax, no.
Future presidents can unilaterally undo EOs. Congress can by normal legislation process. Courts can strike it down "unilaterally", and hold a royal rumble all the way to the SCOTUS. Because it's not law. It's interpretation and marching orders, implementing existing law.
Suppose Congress makes a law saying "Each State shall be given between two and ten turnips per year by the Department of Education." The POTUS can write an EO giving 10 turnips to North Dakota, 9 to Florida, and two to everyone else. The next POTUS can give 10 turnips to every state in the union, or two to every state in the union. The law sets the limits, and EOs (most are fairly mundane) implement it and must play within those limits.
President doesn't have the right to change taxes, that's Congress. No new or changed excise taxes. Maybe fees, if they're not set by law. But if they're high enough, it can be taken as legally akin to a poll tax. That is, a tax on a Constitutional right. That's not kosher either.
So, unilaterally, he can have the lawyers find the fullest extent of the law and apply it. Like daily FFL audits. Or ban any import of firearms, ammo or accessories. But that's about it. So, "annoying", but not "express or indirect banning domestically" stuff.
