Any parameters -almost by definition- will need to be re-visted at some point and changed. Looking at the Properties panel, there should be a section where Edge 1 and Edge 2 are clearly displayed. See the way Solid Slab's Geometry section has its Width, Length, Height parameters clearly visible, not hidden.

Forcing the user to delve into the Segments section of the PP is really non-productive and slow. Forcing the user to drill down into the Segments section and try to figure out what length parameter to change is really a big time waster.

Also, 'Length' should read 'Edge 1'(?) in the Segments section. This would match the input parameters in the Place Block dialog.

See previous discussion