Try this code to see if it is what you are looking for.

#!/usr/bin/perl -w

my $data = 'reference.txt'; 
open INFILE, '<', $data;
my %hash = ();
while (<INFILE>) {
    chomp($_);
    my ($id,$description)=split(/\t/);
    #print $id,' << ',$description,"\n";
    $hash{ $id } = $description;
}
#print "\n";

#while ( my ($key, $value) = each(%hash) ) {
#      print "$key => $value\n";
#      }
    
my $data2 = "readthisfile.txt";
open INFILE2, "<", $data2;
while(<INFILE2>) {                    
    chomp($_);
    @parts = split /\t/;
    print "Original \t",++$i,': ',$_,"\n";
    print "Replaced \t",$i,': ';
    foreach $parl(@parts){
        if ($parl =~ m/(.*\{)([0-9]+)(\}.*)/) {
            $parl = $1.$hash{$2}.$3 if exists  $hash{$2};
            }
    print $parl,"\t";
    }
    print "\n";
                    }
[download]

perl "D:\Temp\repalce1.pl"
Process started >>>
Original     1: ABCDE
Replaced     1: ABCDE    
Original     2:                                                       
+                                                                     
+                                                     
Replaced     2: 
Original     3: +P237S    S{301609239}                                
+                                                                     
+                                                                     
+                          
Replaced     3: +P237S    S{kitchen}    
Original     4: +R372W    W{114672573}                                
+                                                                     
+                                                                     
+                          
Replaced     4: +R372W    W{study room}    
Original     5: +K576R    R{20531742}    R{89242146}                  
+                                                                     
+                                                                     
+                                    
Replaced     5: +K576R    R{living room}    R{terrace}    
Original     6: +R1059Q    Q{126723431}    Q{6934272}    
Replaced     6: +R1059Q    Q{126723431}    Q{6934272}    
Original     7: 
Replaced     7: 
Original     8: STRKE
Replaced     8: STRKE    
Original     9: 
Replaced     9: 
Original     10: +T216I    I{301781720}    I{148237434}               
+                                                                     
+                                                                     
+                                       
Replaced     10: +T216I    I{balcony}    I{148237434}    
Original     11: +V275I    I{149632297}    I{47224534}                
+                                                                     
+                                                                     
+                                      
Replaced     11: +V275I    I{149632297}    I{47224534}    
Original     12: +R13H    H{126333615}                                
+                                                                     
+                                                                     
+                          
Replaced     12: +R13H    H{126333615}    
Original     13: +F113L    L{301781720}    L{148237434}               
+                                                                     
+                                                                     
+                                       
Replaced     13: +F113L    L{balcony}    L{148237434}    
Original     14: +G135S    S{147902132}    S{47224534}    S{125864042}
+    S{107921834}                                                     
+                                                                     
+                                                              
Replaced     14: +G135S    S{147902132}    S{47224534}    S{125864042}
+    S{107921834}    
Original     15: +T307A    A{224050516}    A{126333615}               
+                                                                     
+                                                                     
+                                       
Replaced     15: +T307A    A{224050516}    A{126333615}    
Original     16: +L217F    F{149632297}    F{147902132}
Replaced     16: +L217F    F{149632297}    F{147902132}    
<<< Process finished.
================ READY ================
[download]