I am fairly new to reading kanji and grammar, and I just learned that "入る" is pronounced "はい" because it is an okurigana. My question is, are all okurigana pronounced in their "okurigana" way regardless of which hiragana follows the kanji? For instance, are "入う", "入ざ", and "入ふ" all pronounced "はい"?
You seem to have a fundamental misunderstanding about okurigana.
The reading of 入る is はいる.
入る is not an okurigana, but it contains an okurigana which is る.
kanji👇 okurigana👇 入 る
"Okuri" means something like "follow-on; accompanying", and "gana" is kana (katakana/hiragana) in rendaku. Therefore, okurigana only refers to the hiragana part after the kanji part.
Basically an okurigana is there to indicate the conjugation of the verb.
- 入る = はいる: enter (plain)
- 入ります = はいります: enter (polite)
- 入った = はいった: entered (past)
- 入れ = はいれ: Enter! (imperative)
- 入ろう = はいろう: Let's enter (volitional)
The okurigana is the hiragana in bold. The kanji part is consistently read as はい. This means there is only a finite number of okurigana patterns, and you cannot use a random hiragana as an okurigana. Simply, 入う, 入ざ and 入ふ are all invalid combinations meaning nothing.
If you are still confused, think that a kanji is like an emoji with a meaning. For example, 😆 = 笑 = "laugh" and 🕺🏽 = 踊 = "danc(e)". Okurigana refers to a short fragment that follows them to indicate a conjugation of the verb.
- 😆ing = laughing
- 笑っている = laughing
- 😆ed = laughed
- 笑った = laughed
- 🕺🏽ing = dancing
- 踊っている = dancing
- 🕺🏽ed = danced
- 踊った = danced
- 😆baz (invalid, meaning nothing)
And these "ing" and "ed" correspond to the okurigana. The 😆 part itself is pronounced the same way.
Note that most i-adjectives and some adverbs/nouns have okurigana, too. Still, okurigana always refers to only the hiragana part.