I may have misunderstood your question.

If you want to dive selectively into a particular sub-hash, why don't you just select that hash by name or index?

 
  DB<27> x 1 @a
0  HASH(0xa7041080)
1  HASH(0xa70411c0)
2  HASH(0xa70413e0)
3  HASH(0xa6f048c0)
  DB<28> x grep /080\)/,@a
0  HASH(0xa7041080)
   'a' => ARRAY(0xa70098d0)
      0  1
      1  2
      2  3
  DB<29> x @a[1]
0  HASH(0xa70411c0)
   'b' => ARRAY(0xa7027540)
      0  1
      1  2
      2  3
  DB<30>
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