Can you take a break from doing veteran difficulty on MW2 do the campaign on an easier difficulty and come back to veteran and still get the Price of War achievement from where you took a break?
What you want to do is go into your save files on the ps3 home
page... find the one that says 'save game and player profile'. take
that and either copy it onto a memory stick or a different ps3
profile on that ps3 (these are on the left most side of the home
page btw). go back into MW2 and start your game again on the easier
difficulty and complete the game, gettin The Price Of War Trophy.
this will overwrite the original version of your veteran save; this
is ok. dont worry. then retrieve your veteran save game from
wherever you put it (ie memory stick or different ps3 profile) and
copy it back onto your profile. when it asks you to overwrite, say
yes and it will get rid of your easier save game and you can resume
your veteran save.
p.s. sorry that was a bit long to read xP