On May 13, 2019, the State Council Customs Tariff Committee released Announcement [2019] No. 2 (税委会公告〔2019〕2号), which indicates that the Customs Tariff Commission has decided to launch exclusion work for US products subject to ad valorem tariffs on a trial basis. According to the applications of Chinese stakeholders, we will exclude some of the products that meet requirements from the scope of ad valorem tariffs on US products. We will take exclusion measures such as temporarily not imposing ad valorem tariffs and refunding ad valorem tariffs collected on products that have the conditions necessary for refunding tariffs. See here for official Chinese version of the attachment 对美加征关税商品排除工作试行办法 (Trial Measures on the Exclusion Work for US Products Subject to Ad Valorem Tariffs), which details the process. 

[For an unofficial English translation* see Announcement [2019] No. 2 and attachment: Trial Measures on the Exclusion Work for US Products Subject to Ad Valorem Tariffs. *The unofficial translation was prepared by the US-China Business Council and is used with their permission.]