Yes, it is "doable" later.  This can't be done in the PERC BIOS, but it can be done in OMSA (OpenManage Server Administrator) from within the OS. One thing to keep in mind is Windows 2TB "boot disk" limit on BIOS-enabled systems.  If you plan to put 4x4TB disks in a RAID 10, that ~8TB "disk" must be converted to GPT and BIOS set to UEFI as the boot mode.
I am thinking of setting up a 4 physical disk RAID 5 array on my new PowerEdge T320.  This should give me enough space to last a long time.  I will have two empty HD slots.  If I need more space later, will I be able to add one or two additional physical disks without losing the data already on the virtual disk?  If so, how?  I did not see a way to do this in the Perc 710 manual.    Thanks, Andrew
Perc 710 Add physical disk to RAID 5 Virtual Disk and keep data