Is there a way to replace re-sized images?

Question

I have several images (640 x 480) that I have placed into a PDF. When I use the Object TouchUp Tool, (right-click and choose "Place Image...") they come in WAY too big for the layout, so I scale them down to fit. Now, I need to replace those images with new ones (also 640 x 480).
1) Is there a way to replace the images, (Right-Click on the image to be replaced > "Place Image...") so that the new images are placed at the same dimensions (and hopefully position) as the scaled old images, instead of having them come in HUGE again and manually scaling them down and re-positioning them?
2) Or, at least, is there a preference dialog somewhere that I can define a specific dimensions for the images to be imported at, regardless of their resolution outside of acrobat.
I realize I could create smaller thumbnails and place those in the PDF instead. However, the person who will be responsible for replacing the images isn't very computer savvy, and it would take longer for them to save thumbnails then to just place the image directly into Acrobat and scale them down.

Answer 1

I want to AVOID scaling the new pictures (and in an ideal world, I'd also like to avoid re-positioning) manually. Example, I have a window sticker PDF for a silver car with 3 pictures in it, a front, rear, and interior. When initially placed into the PDF, the pics (640 x 480)for the car were too big for the layout, so I used the Object TouchUp Tool in Acrobat 8 Pro to scale them down to about 150 px wide and position them correctly. Now, we get a new car in. It's practically the same car, but blue. So, the most efficient way to create a new pdf window sticker for the blue car would be to save a copy of the silver PDF and then just replace the silver pics with blue ones.
Practically every other graphical Adobe program on the planet has a way to "replace" or "update" raster images. In my Acrobat 8 Pro travels, it doesn't seem there is a way to do this. I can "replace" (overwrite) the old silver pictures by selecting a pic with the Object TouchUp Tool, then right-click "Place Image..." This will stick the new blue photo in the same position as the old one. However, it still imports in at the giant 640x480 size, instead of the scaled-down 150 px wide size. So, I still need to manually scale the new blue photo down.
Also, I've tried every combination of SHIFT, ALT, CTRL clicking to try to scale the pic from its center. In other words, if I grab the lower-right handle of the pic, the anchor point for the scale is the upper-left corner of the pic... so scaling it like this throws the pic out of position anyway.
So, if anyone has a way to scale a pic from it's center, instead of the corners, please post it!! Even if I could get a dialog box requiring specific numeric dimensions... that would be preferable to having to re-size and manually nudge and smush the pics around to a rough eyeball location every time I need to make a new window sticker for a car (which is a lot)
Cheers!