Hello harryjb,   What you propose will work. First I would always recommend you have a good backup in case anything happens during the RLM. If you do get a backup then you could delete the array, add drives, create array and restore or at least have it to fall back on in case anything happens.
Have a raid 0 virtual disk composed of 2 x 1Tb SSD and want to convert to raid 5 by adding more disks  Tried to reconfigure but noticed the option to add new physical disks is not available.  Looked up documentation on perc H330 mini and found this controller does not support RLM.  As we also have a r730 with a H730 mini I was wondering if it would be possible to transfer the physical SSDs to that server and perform the reconfiguration and them move them back to the r630.         
dell r630 perc h330 mini virtual disk expansion