[gentoo-user] Again, emerge -e @world related questions...

Hi,

what could fail, when doing the change to PIE-enabled applications
on base of the regular updates?
Compilation may fail, if libs are included and not flagged as to be
recompiled, which are of the "old standard"...
What else can fail? What may be the worst scenario?

Is there a way to do a "emerge -e @world" but only for the system
applications?

Would it be possible to do a "emerge -e @world" for the system
applications and then update the rest of the applications via the
regular updates of the system (and recompile failing components
manually because one obviously already know the reason) ?

Do I have to do a "emerge -e @world" from a certain kind of
"reduced system" i.e. starting the system without a desktop
first or boot into an even more reduced state aka "maintance
mode" (via grub) and make the disk rw by hand?
Or is even a much more esoteric doing necessary?

Cheers
Meino