perldoc says "The foreach loop iterates over a normal list value and sets the scalar variable VAR
$var->{$y} isn't a variable.
the modified hash structure is not required
Did you just say it's not necessary to change $var->{$y}? Then why do you do it?
t doesn't mention aliasing.
Maybe, but it does mention the variable acts as an alias.
If any element of LIST is an lvalue, you can modify it by modifying VAR inside the loop. Conversely, if any element of LIST is NOT an lvalue, any attempt to modify that element will fail.