Although I have never tried it, I have read the manual pages of both resolv.conf and resolver, and I found the following line which would interest you :-
This is from the resolv.conf manual page.
The resolver is a set of routines in the C library that provide access to the Internet Domain Name System (DNS). The resolver configuration file contains information that is read by the resolver routines the first time they are invoked by a process.
And this is from the resolver manual page:-
The res_init() function reads the configuration files (see resolv.conf(5)) to get the default domain name, search order and name server address(es). If no server is given, the local host is tried. If no domain is given, that associated with the local host is used. It can be overridden with the environment variable LOCALDOMAIN. res_init() is normally executed by the first call to one of the other functions.
So I guess you can read the resolv.conf file using resolver but I could not find any method that would actually write back to it.