How to rename from:
VAR1_1F_text.txt VAR2_1F_text.txt VAR3_2F_text.txt
to
1F_VAR1_text.txt 1F_VAR2_text.txt 2F_VAR3_text.txt >
You could also use Magnar Sveen's multiple-cursors from here, github link.
Switch to writable dired, select the files you want to rename, M-x mc/edit-lines. This should create multiple cursor each with its own kill history.