是否可以禁止对PDF进行自动编号?

好的.为您的输出格式添加一个format变量，并在figref中为该格式添加一个处理程序.使用RStudio预览版，您可以使用format <- knitr::opts_knit$get("out.format")，但是对于发行版，则需要手动进行设置.
然后在figref()中添加所需的输出...

Sure. Add a format variable for your output format and a handler for that format within figref. With RStudio preview edition you could use format <- knitr::opts_knit$get("out.format") but with the release version you'd need to set it manually.
Then in figref() add whatever you desire for the output...

    if ( format == "latex" ) return( caption )
    if (!missing(caption)) {
    --- >8 ---

我个人将使用预览版和switch语句进行处理.遵循 https://***.com/a/27321367/173985 .

Personally I'd use the preview edition and a switch statement for the handling. Along the lines of https://***.com/a/27321367/173985.