Any alternative to destroying the pool

I have a box with 4 x 6TB drives in RAIDZ2 that I want to expand to 8 x 6TB drives in RAIDZ2.  
AFAIK I have to destroy/recreate the pool and reload everything from backup.

Is there any alternative that I might have missed?

I'm looking at a day or so downtime, and a bit of risk, so I'd love to avoid it if possible.
Thanks in advance for any advice/suggestions.