Replacing a substring at a specific position

[paarfal]

Hi all, need some help.

I want to replace the second character in a string, regardless of what character that is.

If I try the replace the second character with the (substring 1, 1) all instances of that character gets replaced.
I just want to replace the one sitting at position 2 in the string.

Ex Good -> Gxod, not Gxxd

Thanks in advance

Patrik