substr is great for this kind of problem:

   substr($foo,5)=~/HLAG/;  # Only beyond the 5th char
   substr($foo,10,100)=~s/narf/poit/g;
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And so on. The nice thing is you can contain the end of the match as well as where to start.

Afterthought: This bind-operator trick can also be used with reverse for nonsense like:

   (reverse $foo)=~/dlroW/;
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But this doesn't work with s///, of course.