[Steve W]

From the definitions :
FIX-IT-WINDOWS – Two 5-hour work periods following the deadline for shipping the robot, or following the close of a regional competition, in which ALL teams may manufacture parts in preparation for future competitions.

Straight from the rules. The Q&A is misleading in their answers. According to the rules you may build and bring with you to competition 25 lbs.

<R29> Teams may bring a maximum of 25 pounds of custom FABRICATED ITEMS (SPARE PARTS, REPLACEMENT PARTS, and/or UPGRADE PARTS) to each competition event to be used to repair and/or upgrade their robot at the competition site.

However : <R17> During the “FIX-IT WINDOWS” following the shipment of the robot: During this period, all teams may utilize one or two 5-hour FIX-IT-WINDOWS to manufacture SPARE and REPLACEMENT PARTS and
develop software for their robot at their home facility. Fabrication of UPGRADE PARTS is not permitted during this period.

Then : <R19> At the competitions: Teams are allowed to repair, modify or upgrade their competition robots while participating in a competition event. To support this, teams may bring SPARE, REPLACEMENT and UPGRADE PARTS and COTS items to the competitions (within the limits specified in Rules <R28> and <R29>).

From all of this I believe that you can build and bring the bumpers with you to competition as they must weigh under 15 lbs. There are more rules to support building them after end of season than there are to say you can't. I have yet to see it stated that the Q&A's are official. That is what the updates are for. I had someone last year tell me straight up that they enforce the rules not the Q&A.

It is still your call on how you handle the situation.