If you just want to remove them or, say, replace them with underscores, this may be just as simple as

s/[^[:print:]]/_/g;
[download]

otherwise if you want to replace each one of them with a string of your choice, you could build up a suitable hash and then

s/[^[:print:]]/$hash{$&}/g;  # Some people dislike $&
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It's not entirely clear to me if you have such a list or if you're searching one. If you have one only for a limited number of chars, you may want to

s/[^[:print:]]/$hash{$&} || '_'/ge;
# or 
# s/[^[:print:]]/exists $hash{$&} ? $hash{$&} : '_'/ge;
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Or else you may want to use some URI escaping package e.g. URI::Escape.

Update: reading Joost's reply, I realize that I may have completely misunderstood your question.