Upgrade all plans on specific package

The easy answer is edit the package itself from within WHM. When saved it'll upgrade all accounts that use that package. But, there is no option there to change the package name if you wanted to.

There's a post here about editing the package name that should help. http://forums.cpanel.net/f7/packages-67244.html

 

And you've moved them already, so no way to upgrade the accounts there then move them over I guess.

I agree, it would be nice to see the packages listed on the Modify Multiple Accounts page. I'm not sure why they couldn't add something for this to that page, you might want to log an enhancement request on bugzilla for it to be considered.

Looking at that page you should be able to select "search by reseller/owner" and hit the "select matching users" button to select these new accounts, assuming the "owner" is still a name from the old server and different than any on your server. That would give you what you seek if these new accounts all have the same plan and owner.

Then select the settings at bottom and save.