In Midnight Commander the move/rename operation is used with the same dialog. But if you just want to rename a part of your filename you always have to rewrite the complete new filename into the dialog window.
Normally you press
F6 to open the move/rename dialog. That looks like this:
You can now just start writing your new filename and it will be renamed. But if you just want to rename a part of it you have to press
Shift + F6 to get this dialog:
Now you can get to your desired position with the arrow keys and just rename the part of the filename you want.