The most noticable difference between Gentoo Linux and Sabayon is the package-manager entropy. So transforming Sabayon -> Gentoo is just about using (the ready to use delivered) portage to compile gentoo-like your own flavoured packages. The transforming vice versa Gentoo -> Sabayon is a little bit more trickier.

Steps to transform Gentoo to Sabayon

• Install the entropy-terminal-frontend: app-admin/equo

rechner ~#> emerge app-admin/equo -atv

• add a sabayon-repository:

rechner ~#> echo "repository = sabayon-weekly|Sabayon Linux Official Repository|http://pkg.sabayon.org|http://pkg.sabayon.org,sabayon.org" \
> /etc/entropy/repositories.conf.d/sabayon-weekly 

• fill System database:
  when following message apears, the system-database

rechner ~#> equo upgrade 
>>  !!! System database not found or corrupted, running in safe mode using temporary, empty repository
>>  @@ Calculating System Updates...
>>  @@ Calculating dependencies ...

to fix that: create a file /etc/entropy/sets/install_base and fill it with all installed files.

rechner ~#> mkdir /etc/entropy/sets
rechner ~#> touch /etc/entropy/sets/install_base