🚀 go-pugleaf

You're problem is that "every page item" of a document doesn't include every
page item -- it only includes those directly on pages. So you'll miss inline
items and grouped items unless you use the "all page items" property:

tell application "InDesign 2.0.2"
 set theClasses to {rectangle, graphic line, image} --I only want to change
these 
 set SuccessCount to 0 -- to see if anything changes
 tell document 1
  set theItems to all page items
  repeat with theNumber from 1 to (count of theItems)
   try
    if theClasses contains class of item theNumber of theItems then
     if stroke color of item theNumber of theItems is swatch "PANTONE 315
CV" then
      set stroke color of item theNumber of theItems to swatch "PANTONE 315
CVU"
      set SuccessCount to SuccessCount + 1
     end if
     if fill color of item theNumber of theItems is swatch "PANTONE 315 CVC"
then
      set fill color of item theNumber of theItems to swatch "PANTONE 315
CVU"
      set SuccessCount to SuccessCount + 1
     end if
    end if
   end try
  end repeat
 end tell
 log SuccessCount
end tell

As in your script, you'll see the stroke and fill colors aren't the same,
BTW (CV v CVC).

Another possibility is to use the delete command, assuming no imported
objects use the color:

tell application "InDesign 2.0.2"
 tell document 1
  delete swatch "PANTONE 315 CV" replacing with swatch "PANTONE 315 CVU"
 end tell
end tell

-- 
Shane Stanley,  sstanley@myriad-com.com.au