Update: Yes, you can do it but it's not immediately obvious and is limited to simple keyword lists. Try this:
Containing Text: DOSEX "=C:\string_to_search.txt" AND "FPGA Rev 0x16"
As long as your keyword list is simple, ie as you describe NS123456 NS98765, etc., this will work as they'll be converted to a DOS style expression:
which is equivalent to:
NS123456 OR NS98765
Why does this work?
It works because DOS Expressions allow compounding of file lists (file lists with file lists) and concatenation of file lists, e.g.
Ultimately version 8 of the product will accept a new keyword
FILELIST so that you can do something like:
FILELIST "C:\string_to_search.txt" AND "FPGA Rev 0x16" with Boolean expressions.