how about an option under the "Actions" drop-down, that would reverse the selections.
for instance, i have several hundred files i wish to insert a character at position 9 and several hundred others i wish to insert this character at position 10.
once i select/deselect the files to do one operation, i merely would reverse selection and all files that were not selected become selected and all files that were selected become unselected.
then, i can up the 'at pos.' number and complete my renaming.
the work-around is to change an attribute or time/date stamp and then sort based on that, but merely reversing selection would be faster and not require that i change dates/etc....