I'm rather sure, you won't lose your steam of an old /home drive. The point is the old settings for KOrganizer (Kontact) to a newly installed KDE and its components.
What you can try is to keep a backup from your old home, then do a completely new install and join the steam parts to the new /home drive or path. That is the way I would try it.
The KDE basics in your /home/user directoriy are the .files and the .directories which are new. Steam could be independent of those KDE files and directories.
If you are lucky, all steam settings are in one directory only.
For Kontact and KOrganizer, you can import old data.
-Linuxfluesterer (I love KDE ...)
I really hope, that by the Brexit (poor Britain), TTIP will be finally prevented. But don't get tired to talk to your local politician to open eyes for danger to democracy because of TTIP