In the Restrictions section of a Blueprint, you'll find the option to "Prevent Changes to Passcode". This feature is useful if you have shared devices where multiple people need to know the passcode or if you have a public-use device like a kiosk where you don't want any passcode at all.
If you want to set up a device with no passcode, leave "Require Passcode" turned off and "Prevent Changes to Passcode" turned on. This prevents anyone from creating a passcode on the device.
If you want to set a passcode and make sure it doesn't change, turn on "Require Passcode" first and save the Blueprint. Next, set a passcode on each device. Last, turn on "Prevent Changes to Passcode" in the Blueprint. Now you can be sure that each device will keep the passcode you just set.
If you have turn on both "Require Passcode" and "Prevent Changes to Passcode" at the same time you may see "Security: Out of date" on the Blueprint status. This typically means that the device is trying to update it's passcode requirements but it's prevented by the restriction. No problem! Go back to the Blueprint and turn off "Prevent Changes to Passcode". Wait a few minutes for the security settings to show "Applied" and then turn "Prevent Changes to Passcode" back on.