Your requst does not compute.
If you have an FS2002 model, that was built using the FS2002 SDKs, just copy it over to Fs2004.
If you want FS2004 eye candy, though, like the added animations, etc., then you're in trouble, because you need to modify the source file.
Now, because there were some changes between FS2004 and FS2002 graphics, depending on what values were used for certain texture effects, then yes, modifying some textures might be in order.
CAn you explain better what you're trying to accomplish?