This should help you find a less chaotic direction. The code is not complete and some bits are not along your wish, but the code is plastic.

You need to improve the value transformation and commation-commification function (rc in the code). 1024 MB is 1073741824 bytes (1024 ** 3), not 1024 * 1000 * 1000.

As for the comma or commas, there might be such a printf option. I'm not sure, but wouldn't be surprised.

This function will also integrate nicely with translation to other measure bases (GB or whatever).

sub rc {
    my $n = int shift()/1024;
    $n =~ s/(\d+?)(\d{3})$/$1,$2/;
    return $n;
}

s/([^:]+:)\s+(\d+)\s+KB/
    sprintf "%-14s%10s MB", $1, rc($2)/e;

s/^\=+$/"=" x 68/e;

my $IMCfmt = "%-17s%17s%17s%17s";

s/^(Name)\s+(Mem Used)\s+\(KB\)\s+(HWM Used)\s+\(KB\)\s+(Cached)\s+\(K
+B\)/
    sprintf $IMCfmt, $1, $2." (MB)", $3." (MB)", $4." (MB)"/e;

s/^([APPL-|DBMS-|FMP_|PRIVATE|DB-]\S*)\s+(\d+)\s+(\d+)\s+(\d+)/
    sprintf $IMCfmt, $1, rc($2), rc($3), rc($4)/e;
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I FORGOT: I used the -p switch on the command line instead of the -n. (That's where all the prints are.)