It is possible to perform many special stains and combine with
immunostains.  I have done both PAS stains and Feulgen stains with
immunostains.  General guidelines - if you need antigen retrieval, do so
before beginning other stains.  For either PAS or Feulgen, which use acid
hydrolysis steps,  perform the special stain first.  After the special is
complete, then follow with the immunostain.  You will find that the acid
hydrolysis in both of these methods will give some degree of "antigen
retrieval" - a fact many of us observed and exploited long before the
modern retrieval techniques became fashionable.  Therefore you may be
able to reduce total antigen retrieval times and/or temperatures.
Al Floyd