The package yamlme (https://kamapu.github.io/yamlme/) provides the object class rmd_doc in R to store and share document templates for Rmarkdown. The package yamlme includes functions defined to read and write Rmd files and to modify content and settings of such documents. You can, for instance, exchange yaml headers and content between documents and modify headers in existing templates. In conclusion, you can use yamlme to produce documents from plain R code.
Do you find it interesting? Then follow the project and take a look to this vignette: https://kamapu.github.io/yamlme/articles/yamlme-intro.html