This is from our internal help system, created with the advice of Lynn. I have used it many time successfully, but there are no guarantees, hence the warning of having a good backup.
 
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UPDATE PRICES
 
This can also be used to update any other elements of the existing data files.
 
Create a comma delimited file with the Item Number and base price (and/or anything else you want, but you always need Item Number)
 
Make a backup and get everybody out of DBA.
 
Make sure you have a good backup.
 
Delete the following files:
    BKICEMTR
    BKICELOC
    MTICEMTR
 
Rename the following files:
    BKICMSTR to BKICEMTR
    BKICLOC to BKICELOC
    MTICMSTR to MTICEMTR
 
Run the DE Inventory Error report to confirm all copied properly
 
Import the file indicating Replace
 
Run the DE Inventory Error report to confirm you haven't introduced errors
 
Copy the following files:
    BKICEMTR to BKICMSTR
    BKICELOC to BKICLOC
    MTICEMTR to MTICMST
 
 
How this works.
 
The first set of files (that gets deleted) are the temporary data import files that were created last time there was an import.
 
The second set of files (that get renamed) are the live inventory files. By renaming them, it puts all your existing data into the data import location.
 
Importing the new data then modifies only the part that is changed.
 
And the third set (renaming back) makes the temporary data import files the live ones.
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The location of the files is your company datafiles, and there will be a .Bxx extension appropriate to you company number.
 
There's no reason why you couldn't actually do this ahead of time, save the newly created files with a .new extension and then restore the original files from your backup. When the time comes to do the price change, delete the 3 old files and rename the ones with a .new extension to .bxx

David -
 
I was ready to give you an A+ for documentation until the very end.  Since these files contain dynamic information such as Units On Hand, you can't do it ahead of time and then dump the files in when you are ready.  It has to be real time.  
 
But otherwise, exactly right and an excellent explanation of what is happening.