To identify text/strings in multiple files and replace them in multiple files simultaneously use the following command:
~$ find ./ -type f -exec sed -i 's/text/text2/g' {} ;
Note that the path of the files is determined in the second block in: ./
The searched and replaced text will be placed in place of the word: text
The text to be added in place will be placed in place of the word: text2
Remember to preserve all other attributes of the command by observing the position of quotation marks, bars, etc.