Given the following file:

*** begin file ***
old_word
OLD_WORD
oLd_wOrd
olD_worD
*** end file ***
 
Is there a substitute command that 
will transform the file to:
 
*** begin substituted file ***
new_word
NEW_WORD
nEw_wOrd
neW_worD
*** end substituted file ***
 
That is to say, the replacement text 
will presereve the original.