Last weekend I had to do exactly that, taming the monstrous cliffhanger upgrade of my MythTv system that still was running a kernel 2.6.15 and hasn't really seen much change since 2009.

I don't think any other distro would have allowed me to upgrade the system without a reinstall. Even though I screwed up because I didn't RTFM and didn't install everything necessary for booting the system with OpenRC, I still could salvage the system by booting with a rescue stick (based on Gentoo of course) and chrooting into my system and fix it this way.

Now it's running a current kernel and it is ready for the installation of the new digital receiver card.