Convert On-Prem AD Users from Office 365/Azure AD to In-Cloud accounts

I have tested this scenario half a year ago because I have a client who will need the same. Worked out well. Please try this in a lab environment first.

#Requirements: Managed domain, Global Administrator, Domain Admin, Active Directory Users and Computers, AD Connect, PowerShell-modules MSOnline & ADSync

#Connect with MSOL
$credential = Get-Credential
Connect-MsolService -Credential $credential

#Check DirSync status
Get-MSOLCompanyInformation | select DirectorySynchronizationStatus

#Backup all ImmutableIDs of federated users

Get-MsolUser | select userprincipalname,immutableid | sort userprincipalname | Export-Csv -Path $env:USERPROFILE\Desktop\ImmutableIDs.csv -NoTypeInformation -Force

#Migrate synced user to cloud only
Step 1: Disable DirSync
Set-MsolDirSyncEnabled -EnableDirSync $false
Step 2: Nullify ImmutableID !!! Make sure you add quotation marks to $null
Set-MsolUser -UserPrincipalName user@domain.com -ImmutableId "$null"
Step 3: Move nullified users to non-synced OU
Step 4: Enable DirSync
Set-MsolDirSyncEnabled -EnableDirSync $true
Step 5: Force AD Connect sync
Start-ADSyncSyncCycle -PolicyType Delta

#Revert migration of user
Step 1: Disable DirSync
Set-MsolDirSyncEnabled -EnableDirSync $false
Step 2: Move user to original OU
Step 3: Put back the ImmutableID of the user
Set-MsolUser -UserPrincipalName user@domain.com -ImmutableId "ID"
Step 4: Enable DirSync
Set-MsolDirSyncEnabled -EnableDirSync $true
Step 5: Force AD Connect sync
Start-ADSyncSyncCycle -PolicyType Delta