Through Alt-click I can hide some parts everywhere in VAB/SPH or VAB+SPH.
@linuxgurugamer, Is it possible to include possibility to hide some parts only at specific category in VAB/SPH (if parts appear at multiple categories) ?
Also, If it's "not going to Blizzy" then may be checkbox at difficulty settings for "hide Janitor's Closet outside of the VAB/SPH" ?