[CentOS] renaming mdadm name

Hi

I have a disk which two of the partitions are part of a RAID1 setup.  I'm
trying to rename the the second raided partition
mdadm -E /dev/sdc4
/dev/sdc4:
          Magic : a92b4efc
        Version : 1.2
    Feature Map : 0x1
     Array UUID : 83d7657b:ebfddcb7:36b0fa14:d29a350c
           Name : oldname:2
  Creation Time : Tue Aug 30 15:25:10 2016
     Raid Level : raid1
   Raid Devices : 2

 Avail Dev Size : 486696960 (232.08 GiB 249.19 GB)
     Array Size : 243348480 (232.08 GiB 249.19 GB)
    Data Offset : 262144 sectors
   Super Offset : 8 sectors
   Unused Space : before=262056 sectors, after=0 sectors
          State : clean
    Device UUID : 97aba979:dd4cf85c:f6dbf4f6:f1e9ccab

Internal Bitmap : 8 sectors from superblock
    Update Time : Fri Sep 23 14:21:00 2016
  Bad Block Log : 512 entries available at offset 72 sectors
       Checksum : 749e26a8 - correct
         Events : 7319


   Device Role : Active device 0
   Array State : A. ('A' == active, '.' == missing, 'R' == replacing)

For the first partition I stopped the RAID using
 mdadm --stop /dev/md127

and then reassembeld using

 mdadm --assemble /dev/md127 --name=newname_boot --update=name /dev/sdc2

The first partition was easy as the system had started the RAID, but the
second parition the system does start, and when I try to assemble it, it
tells me it's already active:-

 mdadm --assemble --uuid=83d7657b:ebfddcb7:36b0fa14:d29a350c
--name=newname2 --update=name /dev/md2 /dev/sdc4
 mdadm: Found some drive for an array that is already active:
/dev/md/oldname:2

So any ideas on how i can rename this ?

Thanks

Phil.