Question: Are there any specifications for designing a PCB layout in regards to the conformal coating process?
I can locate acceptance criteria in IPC-CC-830/IPC-HDBK-830 /MIL-I-46058C for coated PCB assemblies, but little information related to the PCB design end.
Answer: IPC-2221B, Generic Standard on Printed Board Design, page 37, Section 4.6.2 Conformal Coating, has the information you are looking for relative to the application to printed circuit boards and what should be considered. In Section 4.6.2.1, Conformal coating Types and Thicknesses will get into the different types of coatings and their functionality.
All of it is too large to add to this post, but you should have a copy of IPC-2221 in your library for help in designing PCBs.