When Can You Avoid Redeploy of Domains with Tools Upgrade/Patch?

For Tools 8.58+, FS/SCM 9.2.046+, are there any circumstances where you can apply a dpk patch, creating a new PS home, without rebuilding / recreating domains (PIA, Web, App)

For example, if I'm on 8.5x.10, and we want to go to 8.5x.20 tools, I thought we just needed to repoint the 3 domains to the new PS_HOME, but one of the team in a recent helpdesk ticket indicated that this was not the case (we'd need to redeploy PIA).

Redeploying domains, particularly in the era of SSL, is non trivial, so I'd like to avoid it when possible!