The default life expectancy for your clients is set, at least initially, based on the software's Plan Settings. This default Mortality Age preference is used only initially to set the length of your client's timeline.
Once you have created a new client case, this setting becomes only informational. Any changes to your client's life expectancy would need to be made manually on the timeline, as described below.
How to change a client's life expectancy
If you need to change the mortality age of a client, go to the Timeline, left-click on the client’s mortality event and drag it up or down the timeline. Moving a mortality event up the timeline should present no problem. You may need to pause periodically to allow the timeline to redraw.
If you wanted to model an early mortality event you could do this by following this short video; What If: Modeling an early mortality - Video UK – Have a question? (planwithvoyant.com)