For example if you're doing something like a parametric hinge, you want to say fillet an edge you press F to enter that mode select the face drag it to what you think is acceptable, say for this example, it's 2mm. Then personally I think you should be able to enter a name for the fillet radius and it assigns it to the 2mm without entering the change parameter dialog but rather the small box that appears when dimensioning parts of your design.