As KY3 (Paul Adler) notes, "[a] graphic on [Rep.] Eric Burlison's website resembles the Great Seal but replaces the quiver of arrows with an AR-15 style weapon." The question is: Is that legal?

I say yes, for various reasons, but most importantly the First Amendment. The First Amendment protects the right to fly the American flag—that is to say, your own copy of the flag—with a peace symbol attached, see Spence v. Washington (1974). Of course, it famously protects even the right to burn the flag. It likewise protects your right to display a copy of the great seal with some technological updating (unless, of course you're doing so to knowingly impersonate government officials or to otherwise defraud people in various ways).

Here's the video of the KY3 segment on the matter:

And, as a special bonus, with thanks to Wikipedia, the flag of Mozambique: