But as soon as 2010.1 is released, Cooker will reopen and become unstable again. So I'll have to return to the stable branch again.
How to do that? Fortunately other people asked that question, and here's the digest:
Once 2010.1 is official, open your Mandriva Control Center > 'Configure media sources...' and remove all from the list.
Then go to http://easyurpmi.zarb.org and add media '2010.1'. It'll generate a script that handles it all*. It might take zarb a few days before 2010.1 is listed there.
Due to bug #39975 you'll have to run:
urpmi.update -a --force-key
to avoid invalid signing key errors after the rpms are resigned with stable keys.
*or in the command line simply:
urpmi.addmedia --distrib --mirrorlist 'http://api.mandriva.com/mirrors/basic.2010.1.i586.list'
for x86 or:
urpmi.addmedia --distrib --mirrorlist 'http://api.mandriva.com/mirrors/basic.2010.0.x86_64.list'