Question: Below are just 2 example sentences for the general format '[phrase]地给[noun][verb][phrase]'. 

1. 他十分坦率地给我讲了他的故事.
2. 他很不情愿地给了我帮助.

This type of sentence is very common in Chinese. I would like to know if, generally speaking, it is acceptable in Chinese to replace '给' with '替' or '为'. If you are Chinese, would you find that acceptable in most, if not all, cases?

Answer: 
No. The words have different meanings.

Let's look at your first sentence:
他十分坦率地[给]我讲了他的故事 : He openly told me his story.

If we were to replace 给 with 替:
他十分坦率地[替]我讲了他的故事: He openly told his story for me (implying that I was supposed to be the one telling the story).

If we were to replace 给 with 为:
他十分坦率地[为]我讲了他的故事: He openly told his story to me for my sake. 

In general I'm not too sure how you got the idea that they are interchangeable.
他十分坦率地给我讲了他的故事. Okay

他十分坦率地替我讲了他的故事. Okay

他十分坦率地為我讲了他的故事. Okay

他很不情愿地给了我帮助.okay

他很不情愿地為了我帮助。wrong

他很不情愿地替了我帮助。wrong

when u are wondering 給 or 替 or 為, 
Choosing 給。
I come from China.Trust me:)