++ Thanks for the generous feedback.

As I indicated, that was my first Dancer2 code; although, I do have some minimal experience with Dancer, so it wasn't completely foreign to me. I appreciate the heads-up re set vs. setting.

I did an additional test, using config and set (instead of the two setting() calls) and adding an actual config file.

Code change:

get '/my_stuff' => sub {
    my $my_stuff = config->{my_stuff} || {};
    my $x = $my_stuff->{X} || 'not set';
    my $y = $my_stuff->{Y} || 'not set';
    return "X[$x] Y[$y]";
};

get '/my_new_stuff' => sub {
    set my_stuff => {X => 'newX', Y => 'newY'};
    return 'New stuff configured.';
};
[download]

New config file (in the same directory as the code):

$ cat config.yml
my_stuff: { X: 'oldX' }
[download]

Test:

$ curl http://localhost:3000/my_stuff
X[oldX] Y[not set]

$ curl http://localhost:3000/my_new_stuff
New stuff configured.

$ curl http://localhost:3000/my_stuff
X[newX] Y[newY]
[download]

I suspect that's a bit closer to what the OP wants: we'll have to wait and see.