I think what is really troubling you is the ambiguity between setting a symbol's slot and assigning to a symbol in Perl. (not sure if this is proper terminology)

Pure Perl has neither an explicit alias operator, nor an explicit unalias operator.²

So if a scalar variable $a is an alias to $b you can't easily say $a=42 without changing $b , i.e. replacing the alias in the $a -"slot" with a literal 42.¹

But when operating with arrays like @_ you have the choice.

$_[0]=42 is accessing the alias behind, but @_=(42) will replace the content of the slot.

  DB<106> sub repl { @_=(42); print "> $_[0]"; }

  DB<107> $a=666
 => 666

  DB<108> repl $a
> 42
  DB<109> $a
 => 666
[download]

It has already been shown how to access multiple aliases at once (slicing), similarly you can use splice to access multiple slots of an array at once.

I hope the distinction between setting a slot and assigning to an alias is clearer now. :)

¹) But you can always use my $a=42 in a new scope or local $a=42 if it's a package var.

²) like tie and untie