The order of entries in the /etc/mailcap file can be altered by editing the /etc/mailcap.order file. Each line of that file specifies a package and an optional mime type. Mailcap entries that match will be placed in the order of this file. Entries that don't match will be placed later.
mime-support:/ gv:application/postscript netscape:text/html less:text/* emacs:text/*
The above would make any entries provided by the mime-support package (as found in the /usr/lib/mime/packages directory) take priority over everything else. The gv package will be used over anything else when it comes to postscript documents. Netscape will be used for any html documents and less will be used for any remaining text documents. However, since neither netscape or less provide for editing documents, any edit or compose actions will fall through to the emacs rules.
There is currently no way to break out a certain type from a wildcard rule. If, for example, both xv and gimp were to specify gif images but use gimp for jpeg'' images.
Also, I would like to add the ability to specify certain actions in the rules. For example, if netscape were to have an edit rule but I wanted to use emacs for editing/creating html documents, I could place a line like