Learn Swedish: Om framträdandet vore bra skulle publiken inte bua. - If the performance were good, the audience would not boo.

Vore is the past subjunctive form of är (to be), used for hypothetical or unreal situations, much like 'were' in the English phrase 'If it were'. While Swedish has mostly dropped its old subjunctive verb forms, vore remains very common in conditional if-clauses.

Why is the word order skulle publiken instead of publiken skulle?

This is the V2 (verb-second) rule in action. The entire if-clause (Om framträdandet vore bra) counts as the first building block of the main sentence. Therefore, the main verb (skulle) must come second, forcing the subject (publiken) to swap places and come after the verb.

How would we modify this sentence to apply this lesson's focus and say the audience would 'not even' boo?

You would replace inte with the negative focus particle inte ens (not even). The sentence would be: Om framträdandet vore bra skulle publiken inte ens bua. Notice that inte ens drops into the exact same sentence slot as inte, coming right after the subject in an inverted main clause to modify the verb bua.

If we wanted to negate the if-clause instead ('If the performance were not good...'), where would inte go?