The below message will be thrown in console/UI while applying 9418 ppm

Since the login page UI is revamped in this build, customized login page if any will be removed with this upgrade. The old login folder will be renamed to login_old for backup.
Do you want to continue? (Y/N)
If No is given, upgrade process will get cancelled and you can start/run the product as before.
If Yes is given, Customized login page will be removed and it will get reset to default. The old login customization will be renamed to login_old and will be available under <Servicedesk Plus-MSP>/custom/login_Old/Login.html
Which can be customized again by doing the below steps.
Post upgrade >> Move to Admin tab >> Self Service Portal Settings >> "Customize now" option under Customize login page >> Edit and copy all the contents in the old login.html >> Replace/paste the copied content under Login page customization page >> Save it.

Note : It is mandatory to include {{login_form}} tag in the html to save the login page customization.
syntax for login form: {{login_form}}
syntax for login image: {{login_image}}
syntax for product name: {{product_name}}
syntax for product version: {{product_version}}
syntax for Product copyright year: {{copyright_year}}
The above syntax need to be added under <div> tags. For reference you can check default.html available under <Servicedesk Plus-MSP>/custom/login folder