In /etc/portage/package.keywords:

#beryl SVN unmasking:
x11-wm/beryl-core **
x11-plugins/beryl-plugins **
x11-misc/beryl-manager **
x11-misc/beryl-settings **
x11-misc/beryl-settings-bindings  **
x11-wm/emerald **
x11-themes/emerald-themes **

------------------------
In /etc/portage/package.unmask
#beryl
x11-wm/beryl-core 
x11-plugins/beryl-plugins 
x11-misc/beryl-manager 
x11-misc/beryl-settings 
x11-misc/beryl-settings-bindings  
x11-wm/emerald  
x11-themes/emerald-themes 

-----------------------
Make a file ~/beryl-svn-update:

#! /bin/bash

emerge -av x11-wm/beryl-core x11-plugins/beryl-plugins x11-misc/beryl-manager x11-misc/beryl-settings x11-misc/beryl-settings-bindings x11-wm/emerald x11-themes/emerald-themes