my $match = '(some [very] odd value).';
my $replace = '(modified value)';

# escape anything that might be a potential problem.
# note -- we ignore known good values, rather than
# encoding known bad values (so if we don't know about,
# it gets encoded)
$match =~ s/([^\w\s])/\\\1/g;
my $regex = qr/$match/;
my $SomeStuff = 'This is a test string (value); (some [very] odd value).';
$SomeStuff =~ s/$regex/$replace/g;

print $SomeStuff;