[dexangeles]

I know that Sodium acetylide would easily react via Substitution with methyl or primary halides, but...

would sodium acetylide react with an alkenyl halide (eg. H₂C=CHBR) via Substitution also? Or would it be an E reaction?  I'm not sure if a carbon double bonded to another carbon would still be considered primary.

[movies]

No, substitution reactions on vinyl halides don't work.  The carbon halogen bond is stronger because it involves an sp² hybrid on carbon.  Also there is a large steric component to the reaction due to the substituents at the allylic position.