I have TeXLive 2017 installed on Ubuntu under
~/.local/texlive/2017 (the canonical single-user equivalent of
/usr/local/), and would like to do the same for the 2018 version.
I've always used the "expert" GUI mode, but it's not possible to enter the desired paths, because the GUI forces you to use a file section dialog that refuses to show hidden folders. I also tried the "wizard" GUI mode, which has the same behavior.
Has something changed in the 2018 installer?
Note: as I was writing this I discovered that in text mode the installer will automatically detect the previous installation and offers to install the new version alongside it, but the GUI doesn't do this. Presumably I could type in all the paths manually in text mode as well, but I'm fairly certain that I've never used it.