I like golf about as much as the next person, but how about something a bit more expansive:

#!/usr/bin/perl
use strict;
while (<>) {
    my ($timestamp, $number, @rest) = split;
    $number = 0 if ($number > 1000);
    print "$timestamp $number @rest\n";
}
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The solutions above work in place. This one is a filter. To use it do something like this:

./filter < input > output
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But don't make output the same as input or the shell will kill your data.

Phil