Open .TXT file Replace Specific Lines with Cell Values

Daily, I have a large number of .txt files which I need to open and replace the contents of line 8 with a cell value and 9 with the character I. It will always only ever be lines 8 & 9 of the txt file and although line 8 is a changing string, line nine will always be the character I. At present I am doing this manually but life is so short I am looking for a more automated solution.

I do have all the files are listed to be changed within a worksheet, but other than that i m completely stuck. Any help would be greatly appreciated.

Thanks