This is when it is very helpful to have inserted graphics as links. Not only
could you search for and replace the exact filename when the field code is
displayed, but if you just replaced the file itself (substituting the new
graphic in the same location with the same name) and updated the field, you
could save yourself the trouble.
Unfortunately, if the graphic is not linked, you're reduced to a semi-manual
operation. You can copy the graphic to the Clipboard and use ^c to put the
Clipboard contents in the "Replace with" box, but you'll still need to
search through all the graphics and replace only the relevant ones.
If this is likely to happen again, I would suggest that you use Insert |
Picture | From File: Link to File (or Insert and Link) to insert the new
image in one instance. Then select and copy the field code to the Clipboard
and use that for your replacement. The next time you need to replace the
image, your job will be easier.