Is it possible to reset a task deadline after a user accepts the task?

There is a work around.
Information we know:
Task has a deadline of 5 days, once the user accepts the task.
tp!startTime on portal report is automatically updated when the user accepts the task.

Solution:
By using queryProcessAnalytics we can identify when was the task accepted by the user and can calculate the due date accordingly.
Now, if you want to show the due date on the task, then it can be easily calculated. Once the user make any interaction on the UI / submits the task, we can capture that due date and all information in process variable to save in database.

If you are showing the due date on the UI, You may need to consider what would you want your user to see when the user hasn't accepted the task.

There is a work around.
Information we know:
Task has a deadline of 5 days, once the user accepts the task.
tp!startTime on portal report is automatically updated when the user accepts the task.

Solution:
By using queryProcessAnalytics we can identify when was the task accepted by the user and can calculate the due date accordingly.
Now, if you want to show the due date on the task, then it can be easily calculated. Once the user make any interaction on the UI / submits the task, we can capture that due date and all information in process variable to save in database.

If you are showing the due date on the UI, You may need to consider what would you want your user to see when the user hasn't accepted the task.