Use the Source, Luke

Regarding 1. - no. A WWW::Mechanize object ISA LWP::UserAgent object, so you can only create a new one if you want to start out with a clean slate.

Regarding 2. - looking at the source, $mech->uri gets updated from the request URI whenever the response indicates success. So either make it that way or overwrite the value yourself:

$mech->{uri} = $my_new_uri;
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Regarding 3. - I've used Hook::LexWrap to wrap my code around some WWW::Mechanize functions while writing WWW::Mechanize::Shell.