Reconfiguring VM's via the API is something I've had to dabble in lately, due to some.... err.. "interesting" behaviour with deploying VM's from templates. Such as the inability to deploy a VM from a template that has a SCSI controller but no disk - useful if using LUN based snapshots, where the .vmdk already exists and you want to move said vmdk into the same directory as the VM after it's been created (and thus can't use the -Diskpath option of New-VM as the path doesn't exist yet). Or if you want to create VM's for use with Citrix Provisioning server, which don't require a local disk but do require a SCSI controller.
While this operation is uglier than I'd like it (most things that involve Get-View and specifications are uglier than I'd like them :-), I found this very good paper which explains the VI object model as applied to VM hardware reconfiguration _much_ better than the SDK documentation does.
Sure the examples are in Perl, but the theory is the same. Combine the document with a listing of all posts by Carter, LucD and halr9000 in the VI Toolkit for Windows community and there's nothing you can't do!