use warnings;
use strict;
use Data::Compare qw/Compare/;

my @target_block = ('Object Type1','NestedObject');
my $target_param = 'Param 1';
my $new_val = 'Hello!';
my $data = do { local $/; <DATA> };

my @stack;
pos($data)=0;
while ( pos($data)<length($data) ) {
	use re '/msx';
	my $repl;
	if ( $data=~m{\G ^ \h* \# [^\n]* (?:\z|\n) }gc )
		{} # comment, nothing to do
	elsif ( $data=~m{\G \s* ( \w(?:[\w\h]*\w)? ) \s* \{ \h*\n* }gc )
		{ push @stack, $1 }
	elsif ( $data=~m{\G (?<pre> ^\h* ) (?<name> [^\n=]+?)
			(?<mid> \h*=\h* ) (?<value> [^\n]+? )
			(?<post> \h*(?:\z|\n) ) }gc ) {
		if ( Compare(\@stack,\@target_block)
				&& $+{name} eq $target_param ) {
			$repl = $+{pre}.$+{name}.$+{mid}.$new_val.$+{post};
		}
	}
	elsif ( $data=~m{\G \s* \} \h*\n* }gc ) {
		die "'}' with no opening '{'?" unless @stack;
		pop @stack;
	}
	else { die "Failed to parse at: \""
		.substr($data, pos $data, 50)."...\"" }
	print $repl//substr($data, $-[0], $+[0]-$-[0]);
}

__DATA__
# comment
Object Type1 {
	Param1 = Foo
	NestedObject {
		Param 1 = Bar   
	}
	# just another comment
}

# comment
ObjectType2 {
	Param1 = Quz = z
	NestedObject {
		Param1 = Baz
} }