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: 
Grammar only:

In the case， "他十分坦率地给我讲了他的故事". We can trim it, then we have "他给我讲故事". You see it ends with "讲故事" (vt+noun). You can also change the order: "他讲故事给我" to make it "vt+noun to someone".

他很不情愿地给了我帮助 can be trimmed as "他给我帮助". You see it ends with "帮助" (noun). It is the object of 给 and 给 is vt.

In case 1, if you replace 给 with 替 or 为, then the grammar is OK but the meaning may be changed. Using 为 is OK because you change "to someone" to "for someone". But if you use 替 here, the meaning is changed to "instead of someone".

In case 2, you cannot replace "给" with other characters since normally if you changed vt, you changed the meaning.
They are not interchangeable. The latter two have fairly narrow meanings in that kind of context: 替 means "on behalf of"; it could be translated as "for," but only in constructions where it clearly means "on behalf of," as in "He did my work for me."

為 wèi means "for the sake of"; again, it could be translated as "for," but only in constructions where it means "for the sake of," as in "She took care of the financial matters, for my peace of mind."

給, on the other hand, has a whole slew of meanings, only one of which is "for." More generally, it can be used simply to indicate the indirect object of a verb, especially (but not exclusively) when that object is the "recipient" of something. That is more or less the way it is used in your example sentence.