In case of the "journal-rss" type of project publishing basically consists of two steps:

1. Transformation of the original muse-source file (`muse-journal-rss-munge-buffer)

2. Marking up of the result of step 2

ad 1

Step 1 assumes the original muse source code. During transformation it refers to the value of the "author" directive (see `muse-journal-rss-entry-template)

ad 2

As part of marking up a file (`muse-publish-file -> ... -> `muse-publish-markup -> ...) the directives are processed.

On the one hand, this means that in step 1 the directives should have been all ready processed, though the directives are only processed in step 2. On the other hand, the order of step 1 and step 2 can not be reversed, because step 1 assumes the muse source format and is not able to work on a marked up file/buffer.

This bug can be fixed as a side effect of implementing feature request #14985.

Until feature request #14985 is implemented you can make use of the following fix:

(setq muse-project-alist
`(("Test-Blog" ("<directory of muse source files>" :default "<file name without extension>")

[... possible other publishing formats for you blog ...]

(:base "my-journal-rss"
:path "<directory into which the blog is published>"
:base-url "<URL to which the blog is uploaded>"
)))))

(muse-derive-style "my-journal-rss" "journal-rss"
:before (lambda ()
(muse-publish-markup (cdr (assoc "title" muse-publishing-directives))
'( ;; Remove leading and trailing whitespace from the file
(0 "\\(\\`\n+\\|\n+\\'\\)" 0 "")

;; Handle any leading #directives
(1 "\\`#\\([a-zA-Z-]+\\)\\s-+\\(.+\\)\n+" 0 directive)))))