Batch replace substring with another in filenames
Unless you need a solution you can use in a script, you can do this directly in Finder.


Select the files you want to rename
Right click one of them, and choose Rename N Items... (where N is the number of selected files)
Choose the Replace Text option in the dropdown
Enter the text you want to replace (".pngEND") and the text you want to replace it with ("_")
Click Rename