How do I model a current or future client disability to see the change in cash flow and any cash shortfalls?

What’s the most commonly used workflow in creating a financial plan? I know you can enter in this software at any point. I just want to understand what path others are following.

I find entering milestone names in place of dates a lot more helpful than entering individual dates. I’m wondering if I can define a milestone date for my client’s date of birth and use milestone name instead of a date. I tried it but the system won’t allow. Any help would be appreciated.