On May 1, 2020, in Cargo Systems Messaging Service (CSMS) #42561433, U.S. Customs and Border Protection (CBP) announced that they would begin approving general ruling applications, including those for component parts, filed pursuant to the Trade Facilitation and Trade Enforcement Act (TFTEA) and 19 USC 1313(b).
The announcement includes the substitution requirements and Declaration of Official required with the application.
CSMS #42561433 can be found here:
https://content.govdelivery.com/bulletins/gd/USDHSCBP-2896f99?wgt_ref=USDHSCBP_WIDGET_2