override dictionary field

Using Ansible 2.0 , is there a way to override a dictionary field in vars file ?

Let’s say I have a role with default dictionary values :
system:

packages_default: [curl, wget, python-software-properties, mc, dvtm, ncdu, vim, htop, iotop, bmon, tree, ntp]
apt_mirror: False

apt_upgrade: False
acl_enabled: False

And then I want to override just 1 dictionary field acl_enabled to True.

If I try the naive way “system.acl_enabled: True” it doesn’t work.

I thought I could use the new combine filter but it gets into a loop :

Both below assignments :

system: “{{ none|combine(system,{acl_enabled: True}) }}”

system: “{{ system|combine({acl_enabled: True}) }}”

results in :
ERROR! recursive loop detected in template string

Any solution ?