use strict;
use warnings;
use Data::Dumper; 

my @array = ("create", "mount", "remove","create", "mount", "remove","create", "mount", "remove","create", "mount", "remove","create", "mount", "remove","create", "mount", "remove","create", "mount", "remove","create", "mount", "remove","create", "mount", "remove","create", "mount", "remove","create", "mount", "remove","create", "mount", "remove","create", "mount", "remove","create", "mount", "remove","create", "mount", "remove","create", "mount", "remove","create", "mount", "remove","create", "mount", "remove","create", "mount", "remove","create", "mount", "remove");

my $nset = 3;
my $every = 10;
my $newelement = "newelement";

my @newarray;
while( @array ) {                            
  for( 1..$every ) {                         # for 10 times
    push @newarray, splice @array, 0, $nset; # push a set onto new array
  }
  push @newarray, $newelement;               # add the new element
}

print Dumper \@newarray;