There's a newer and better (safer) method of upgrading/downgrading system firmware: Daybreak.
Requirement: Latest version of Atmosphere
SciresM says this on Reddit about Choudujournx:
1. It's not safe. It installs and deletes in a way where something goes wrong in the middle of the process you can end up with partially installed updates or corruption. This happens more than you think.
2. It doesn't reliably update the BIS partitions containing package1/package2 correctly.
3. It will brick your device when run on Mariko because it always flashes erista firmware.
4. Its developer does not maintain it and has not been around for a year or so.
Source: YouTube
Requirement: Latest version of Atmosphere
Template public:_media_site_embed_youtube not found. Try rebuilding or reinstalling the s9e/MediaSites add-on.
SciresM says this on Reddit about Choudujournx:
1. It's not safe. It installs and deletes in a way where something goes wrong in the middle of the process you can end up with partially installed updates or corruption. This happens more than you think.
2. It doesn't reliably update the BIS partitions containing package1/package2 correctly.
3. It will brick your device when run on Mariko because it always flashes erista firmware.
4. Its developer does not maintain it and has not been around for a year or so.
Source: YouTube