Resourse assignments in P6 Ver 7

Hi,

I am a new user of P6 version 7. I want to prepare the program with resourses on it. I am not sure what I am doing is correct or not but I am explaining here to you all (Expert & well experienced Planners) for your comments:

I create a material resourse with the estimated production rate of units/day and assign that to the activity. The activity duration type I keep is "Fixed Units/time". Then I give budgeted quantity so the durations are derived from that. If I change the budgeted quantity the durations will change by its own.

Now my problem is, while creating the resourse I set certain production rate for that and I assign to the activity. But if I change the production rate of the resourse, it doesn't change to the assignments by its own. I have to remove the resourse assignment & reassign the same resourse again which is very boring and time consuming task. I am surer there must be some other way to do all at the same time. Can any body direct me how to do that?

Thanks

Nilkamal