G'day madbee,

"So, given a string:"Study Protocol (No.|No|Number) NBXF317N2201", how can I modify my expression in order to extract NBXF317N2201 which is always a combination of alpha-and numbers and is always 12 characters long?"

If that's really all you need to do, just anchor your regex to the end of the string:

$ perl -Mstrict -Mwarnings -E '
    my $str = "Study Protocol (No.|No|Number) NBXF317N2201";
    my ($term) = $str =~ /([A-Z0-9]{12})$/;
    say $term;
'
NBXF317N2201
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