If you want to do songs just like Stan Rogers or Gordon Lightfoot did them (although obviously in the key you can sing them in), that's OK, but not always the most desirable. It's a personal preference issue. Sometimes a rendition that very closely resembles the original or best known version of a song is comforting to those who are familiar with it. Other times it sounds like too much imitation, the "wannabe" syndrome. Conversely, a noticeably different arrangement of a song will be considered by some to be breathing new life into it, by others to be butchering it.

I suggest do what feels natural and best to you. If you really like the way you have heard the song and want to bring that to the audience, stay with the original arrangement. (You might want to avoid any conscious or subconscious attempt to mimic someone else's voice.) In time, you're likely to personalize your rendition to some degree, perhaps changing a word or altering some phrasing here and there. Again, do what feels right. Trying to force yourself to rearrange the song, just like trying to force yourself to slavishly reproduce the original, will dampen the soul of what you're doing. Do it like you want.