Hello! @Johan Andersson
Welcome to the LastPass Community.
Since your account is a LastPass business account. The only way to force a user to change the master password as after a specific time frame will be By using your policies from the admin console. And actually, is the policy that you are talking about "Require master password change"
It will be better to set a 90 days' time frame or a little bit more, but no 365, which basically that's a year.
Once you enable this policy, once the user reaches the time frame, the user will get a message, and it will be forced to change the master password to continue working with LastPass. Unfortunately, we are not able to set a specific notification before that happens. Or at a specific pop-up message in the bold for that user. The only option to work with will be the policy.
Please let me know if you need additional help.
Greetings!
Verlaine | Customer Care