It's really all about your Angle-of-Attack (AOA)
Va "generally" increases as weight increases. This is due to the increase in AOA relative to structural load limit, which as was mentioned, is because of the aircraft's higher AOA. With that, the aircraft will now stall sooner that before in relation to the certification load limit. However, with the modification mentioned perviously, this may have a material effect on the AOA, such that for a given weight the AOA with the modification may have effectively reduced AOA and not increased AOA. So again, in summary, it is all about the AOA. Clear as mud?