not so sure, the USA Cycling rulebook states the upgrading/downgrading rules have been transferred to a policy document which is here:
which turns out to be a really short policy doc:
1.1 Rider Upgrading and Downgrading.
The following are the regulations concerning upgrades and are copied here for reference from the USA Cycling Rule Book.
1E1. General Information
a. Rider upgrades are handled electronically through USA Cycling via the rider’s online account. The request will be sent to the person responsible for the area and/or category.
b. Only races permitted by USA Cycling, or foreign races permitted by a UCI affiliated National Federation will count for upgrading.
c. Riders who are more than halfway through a series may request a waiver of a mandatory upgrade so that they may finish out the series under the conditions below:
i.The series is covered by a single permit and one race director.
ii.The request is approved by the race series director and USA Cycling.
iii. The waiver is granted for a maximum of three event days.
iv. Such a waiver may only be used once per rider per category.
Note that for MTB series, subsections (i) and (iii) are not applicable.
d. Points, experience and rankings for all voluntary upgrade requests may only date back 36 months from the date of the upgrade request.
e. Riders who have upgraded will start begin to accrue points in their new category with a zero balance.
f. Junior and Youth riders are exempt from mandatory upgrade regulations, for points gained in Junior and youth racing. Points gained in U23 and Elite events will be used for mandatory upgrading, up to Category 3.
g. All Rider Upgrade/Downgrade details for Road, Track, Cyclocross and Mountain Bike are found in USA Cycling Policy VIII-Race Category Upgrading/Downgrading.
1.2 Non-Sanctioned Events.
Events not complying with rule 1E1(b), mentioned above, may be allowed with written agreement with USA Cycling may be taken into consideration for upgrading.
That same info is repeated in chapter 1 of the 2019 rulebook.