code:

s/\([C.I,L,M,V,X]+\)\.\([0-9]+\.[0-9]+\)/\\eqref{eq:,(roman-to-arabic \1).\2}/

code:

re-search-forward is an interactive built-in function in `C source code'.
(re-search-forward REGEXP &optional BOUND NOERROR COUNT)

Search forward from point for regular expression REGEXP.
Set point to the end of the occurrence found, and return point.
An optional second argument bounds the search; it is a buffer position.
The match found must not extend after that position.
Optional third argument, if t, means if fail just return nil (no error).
  If not nil and not t, move to limit of search and return nil.
Optional fourth argument is repeat count--search for successive occurrences.
See also the functions `match-beginning', `match-end', `match-string',
and `replace-match'.

code:

(while (re-search-forward "as?" nil t)
  (replace-match (concat (match-string 0) "__")))