My requirement is as below:

We need to give end users to provide us with some conditions,
One of example rule would be:
They can say something like when the client id is XYZ(could be a complex condition here) then consider I need to pay taxes in AB,CD states.

As we have different end users, we can have these rules per end user.

And when we get a web service call, based on the end user we need to pull all these rules and then apply the rules(basically all these rules do a transformation on the incoming request)

I need to a design for this requirement:

At first I thought I can build a UI and db to save all these rules.

But I realised that it would really take a long time.

I found Guvnor as a web application, with which we can provide a UI and these rules will be saved in db.

The confusion I have now is:
Can I tweak the Guvnor source code(locally) to make these rules saved per end user?

Is it doable?

Any suggestions, for the design are welcome.