I WAS MISTAKEN!!!!
My previous post defining how to eliminate this problem was not entirely correct.
Specifically, the problem does recur.
The following is specific to the Mac Pro mid 2012 and does not imply, infer, or suggest that this is empirical for ALL mac models.
I followed my own previous post and produced a backup clone as I normally do.
The problem did once again occur.
Irritated by this I sought an alternate solution and discovered this.
http://support.apple.com/kb/HT4718
Here is the scenario.
I made a Legal clone on an external drive and installed the clone internally.
This caused the problem of duplicate "open with" to occur.
The question is, how do I stop this from happening altogether?
I managed to stop this altogether using this technique.
(Before you use this technique you should realize the following.... this technique is for producing a LEGAL CLONE.... if you are the person who makes a clone and distributes the clone to your buddies thus violating copyright law, then this technique will most likely lead to your arrest as a Felon)
You will need a high speed internet connection preferably Ethernet although WiFi will work albeit much more slowly.
Place your Energy Saver Computer sleep settings to Never. (the montior settings remain as they are)
Restart your computer holding down the Command and R keys.
Select your operating system hard drive, you are doing a Reinstall Mountain Lion.
Follow the onscreen instructions.
This will take no less than 2 hours and in some cases more using an Ethernet connection and longer for WiFi and days for all other connections.
Best advice is to start this process then go to bed. All will happen automatically including a self restart.
This forces the newly Reinstalled system to create a new index file.
(don't forget to reset your preferred Energy Saver settings once completed)
I tested this procedure by once again making an externally bootable backup clone.
The duplicate "open with" problem did Not recur.
I then ejected and turned the external clone off and then remounted it.
The problem stayed away and did not recur.
I have NOT installed the external clone internally to test to see if the problem reappears, but if it does, this seems to be the safest solution.
Fiddling with your executable code via Terminal commands is ALWAYS risky.
This procedure has no risk.
For what its worth.
The reinstall procedure does Not erase or delete any installed applications or preferences.
I once again make this clear, ALL of this is with reference to a Mac Pro mid 2012 running Mountain Lion.
I cannot state for a fact that this is the solution for all Mac models.
All I can say is.... it works for me.