Changing Per Gig Data Plan

I have been getting conflicting information from various customer service representatives on this question, so I figure I would ask someone who might have tried this to let me know if this works.

I just ordered Xfinity Mobile for four phones.

I was thinking of starting with $15/GB data plan and then as we approach end of billing cycle, I would observe the total data usage, and change accordingly.

For example:

1. If we are close to 1GB limit, I would change to the $30/3GB rate.

2. If we have exceeded the 3GB limit and would probably hit 5GB of usage, I would change to the $60/10GB rate.

3. This would rare, but if all four lines are approaching 4GB of usage (each), I would convert all four lines to unlimited.

Has anyone followed this type of strategy and did you succeed in making these types of changes?