Remaining Units as a % of Budgeted Units

Dear fellow Planners

I am looking for a way to manipulate the Remaining Units to be a % of the current budgeted units and to spread this value over the remaining duration of the activity. 

In my current set up it works almost perfectly, when I reschedule the remaining units are being calculated by P6 based on Duration % Complete. However, does anybody know how I might make the Remaining Unites show as a % (taken from Duration % Complete) of the current budgeted units as this number can often change between updates and I don't want to have to calculate the remaining units each time.

I thought this could be achieved through a Global Change but from what I can tell it is not possible to manipulate these fields in Global Change. I may have to resort to an export to excel and do it there. 

Background:

I am using a P6 Programme as a management tool to track a series of small projects (one activity for each project). Each project is has been resource loaded with the Budgeted units assigned to each project. Often, when a project is In Progress the budgeted units may be increased.

Thanks 

Seb