Here we are, I figured it out 
So, if you are in need of the same setup, here is what I did and the explanation.
First, to make my life easier, I installed the Studio Code Server addon
Using the Studio Code Server, I then edited the configuration.yaml to add
cover: !include covers.yaml
I created the covers.yaml file in the same directory as configuration.yaml and edited it.
The content is
- platform: template
covers:
cloison:
friendly_name: Cloison
unique_id: cover.cloison
icon_template: mdi:archive
device_class: shutter
open_cover:
service: cover.close_cover
data:
entity_id: cover.cloison_inv
close_cover:
service: cover.open_cover
data:
entity_id: cover.cloison_inv
Here are the keyword to understand WHAT we are doing.
In the following code, you will find
[EXISTING_ENTITY] : The device you base your new device on. You need to “create” your new inverted blind (for instance) in relation with an existing one.
[NEW_ENTITY] : The new inverted device.
- platform: template
covers:
[NEW_ENTITY]:
friendly_name: [New Entity Friendly Name]
unique_id: [New Entity Unique ID]
icon_template: [New Entity Icon]
device_class: [New Entity Device Class]
open_cover:
service: cover.close_cover
data:
entity_id: cover.[EXISTING_ENTITY]
close_cover:
service: cover.open_cover
data:
entity_id: cover.[EXISTING_ENTITY]
stop_cover:
service: cover.stop_cover
data:
entity_id: cover.[EXISTING_ENTITY]
[New Entity Friendly Name] can be what you want as display Name
[New Entity Unique ID] is a unique ID assigne to your entity. In our case, cover.[new_entity] could be a good id as soon as it is not already in use.
[New Entity Icon] can be selected here : Icons - Home Assistant
[New Entity Device Class] can be selected here : Cover - Home Assistant
Once you edited your covers.yaml file, go to Developer Tools > YAML > CHECK CONFIGURATION
If you don’t have any error, reload the configuration.
You should find your new entity in the list
I hope it will help my fellow HA users to achieve the cover inversion