You will have to precompile your regex someplace before the conditon, basically like

# @a holds a list of string
my @a = ("a", "b", "c", "/", "\[", "\"");

#create a regex that matches every element in the array
my $re = do { qr/(@{[join ("|", map { quotemeta } @a)]})/ };
die "not a regex!" unless ref($re) eq "Regexp";
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You can put that $re into your regex like so

#you don't need to escape ;
... $chosen_C !=~ /^\*.{36};$re;/ ...
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or you can put the whole regex into the variable.

my $re = do { qr/^\*.{36};(@{[join ("|", map { quotemeta } @a)]});/ };
die "not a regex!" unless ref($re) eq "Regexp";

... $chosen_C !=~ $re ...
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Thanks to calin for the "@{[statement]}" trick.