$ cat infile
host bertha-clp-0 {
    hardware ethernet       AA:0A:A0:00:6c:40;
    fixed-address           10.10.10.72;
    option subnet-mask      255.255.255.0;
    next-server             10.10.10.2;
    option routers          10.10.10.1;
    option extensions-path  "bertha.cfg";
    filename                "/agul.clp;
}
host mona-clp-1 {
    hardware ethernet       00:0A:A0:00:20:CC;
    fixed-address           10.10.10.73;
    option subnet-mask      255.255.255.0;
    next-server             10.10.10.2;
    option routers          10.10.10.1;
    option extensions-path  "bertha.cfg";
    filename                "/agul.clp";
}
$ cat script.pl
use warnings;
use strict;

@ARGV == 3 or die qq[Usage: perl $0 file entry name\n];

my ( $name, $entry ) = ( pop @ARGV, pop @ARGV );

{ 
        local $/ = "}";
        while ( <> ) {
                if ( /(?i:host)\s+${entry}-(?i:clp)-/ ) {
                        s|(filename\s+"/).+(\.clp)|$1${name}$2|is;
                }

                print;
        }
}
$ perl script.pl
Usage: perl script.pl file entry name
$ perl script.pl infile bertha kucar
host bertha-clp-0 {
    hardware ethernet       AA:0A:A0:00:6c:40;
    fixed-address           10.10.10.72;
    option subnet-mask      255.255.255.0;
    next-server             10.10.10.2;
    option routers          10.10.10.1;
    option extensions-path  "bertha.cfg";
    filename                "/kucar.clp;
}
host mona-clp-1 {
    hardware ethernet       00:0A:A0:00:20:CC;
    fixed-address           10.10.10.73;
    option subnet-mask      255.255.255.0;
    next-server             10.10.10.2;
    option routers          10.10.10.1;
    option extensions-path  "bertha.cfg";
    filename                "/agul.clp";
}