As shown in the figure: 
I want to change all the file extensions in the folder from .sublime-snippet to .txt
ren *.sublime-snippet *.txt
ren *. (extension to be modified) *. (extension after modification)
Save as XX.bat, double-click to run
PS: Only the file extension of the current folder will be replaced, neither the child folder nor the parent folder will be replaced.
Effect picture: