Windows Azure: Reinstalling Linux without recreating VM

There's no mechanism to re-pave an existing VM. But...

At any time, you can create a new VM from a gallery image (such as one of the baseline Linux images - Ubuntu, CentOS, etc). If you have an existing cloud service (xyz.cloudapp.net), you can simply place your new, clean VM in that cloud service. You'll still need to include endpoint-mapping, but this should be a trivial part of the creation process (especially if you're using PowerShell or the CLI to create the VM). The new VM will have a new VHD (stored in its own blob, independent of the original VM's vhd).

You can also delete your old VM (and related vhd) without deleting the existing Cloud Service.

Just note: If you had attached disks on your original VM (and assuming they had data or files you wanted to keep), you should detach them first (without deleting them). Then, after your new VM is created, you can re-attach those to the new VM.

you have redeploy option, which will install OS again