PS CS with color space set to Prophoto RGB - will ACR change embedded profiles?

Probably a foolish question but my problem is that I have a mixture of files:

1. My own files (all initially RAW (NEF) which I import into ACR as 16 bit Prophoto RGB ).
2. Files from family members and from slide scanning performed elsewhere - they are in 2 groups:
   1. The first of these from elsewhere acquired files were all JPEGs that I converted to Tiffs in Bridge before setting out to edit them-- all unfortunately 8bit and sRGB.
   2. The scanned files were scanned as tiffs but also 8bit and sRGB.

My normal procedure is that I in ACR I have set the files to 16 bit and Prophoto RGB. In PS the same but also to preserve embedded profiles. I have the impression that working with the "foreign" files in 16 bit does give me more room for editing but that I should continue with the embedded profiles.

Is there a way to ensure that the color profiles are not changed in ACR even if the line in the middle below says 16 bit Prophoto RGB (I have PS CS5). I would hate to have to change this line each time I view a file in ACR. I would hate more to loose the editing facilities in ACR as these acquired files do need som special care before they are mixed with my own in our family albums. I prefer the 16 bit Prophoto RGB option for my own files as I like to play with them - i.e. apart from including them in Photo Albums.

I do see that a logical way is to process all the acquired files before going to my own files but it is so much more practical for me to work with a mixture of the files sorted chronologically - a year or month at the time.

I would even consider getting an upgrade to CS6 if this version could help me.

Can someone enligthen me?

Thanks, Git