upgrading macos on external hard drive only?

[kudukudu]

I have a 15" PB running 10.2.8. I also have 250GB external lacie hard drive with a couple of bootable partitions. I have successfully tested my backups by booting off of the external partitions.

Can I test out an upgrade by booting to a mirror on my external hard drive and simply upgrade the external hard drive from 10.2.8 to 10.4? I suspect this will work, but I am asking since upgrades and re-installations of operating systems can sometimes be quirky.

 

[ElDiabloConCaca]

Yes, you can upgrade any of your installations individually. When it comes time to install the update, you will be presented with a list of partitions.