To insert characters into filenames:
Drag the files you want to rename from the Finder to the file table.
Click
and choose Characters.
Click Insert.
Type the characters you want to insert into the “Insert text” box.
Enter the character position at which to insert the text in the “At position” box.
Click Apply.
. In this case a character position of 0 means the text is inserted after the last character, 1 before the last character, and so on. This is useful if each filename has a different length and you want to, say, insert text before the second-to-last character (character position 2).