I wrote:
> I've fixed mbrlabel to be a lot saner about updating the disk label.
> 
> Previously it would trash the existing in-core disklabel with one
> generated from the MBR (Master Boot Record) of the disk. This could be
> suboptimal in many situations.
> 
> Now it won't actually update the disk label (in-core or on-disk)
> unless `-f' is given.

I've just changed this to:
	-w 	write in-core label if changed
	-r	in conjunction with -w, update on-disk label as well
	-f	force write, even if no change detected

The default is to just print what would happen (and not update any label)