This option is gone since KeyShot 7.
CTRL +N and CTRL+I does the same but enables using pre defined template scenes that contains all necessary options like model set with a ground plane, useful camera positions, perhaps combined this as studio(s) and your favorite environment(s).
Instead you can also delete the geometry (edit > delete …) before importing the new geometry, but save as …
I don’t want to criticize your workflow, but show you the benefits of new ways that can save a lot of time previous versions wasn’t capable to do.
Hope that helps or give the right impulse for an workflow update.
Cheers
Marco