Confirmation on gst rate

No... It's not specifically mentioned any codes or supplies. It's only applicable to Job works as per definition under GST. As

“job work means any treatment or process undertaken by a person on goods belonging to another registered person and the expression job worker shall be construed accordingly” [Section 2(68)]

Job works charges As per Notification 20/2019-CT(R) Dt: 30/09/2019. 

i) For diamond related services

• Rate of GST reduced from 5% to 1.5% on supply of job work services in relation to diamonds.

ii) For engineering related services other than bus body bldg.

• The rate of GST reduced from 18% to 12% on supply of machine job work such as in engineering industry, except supply of job work in relation to bus body building which would remain at 18%.