I don't understand the question :)

I think the answer is either-or, pick-one :)

It is based on reading

http://search.cpan.org/grep?cpanid=GUGOD&release=App-perlbrew-0.30&string=PERLBREW_ROOT&i=1&n=1&C=0

our $PERLBREW_ROOT = $ENV{PERLBREW_ROOT} || "$ENV{HOME}/perl5/perlbrew
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139:    setenv PERLBREW_ROOT "$HOME/perl5/perlbrew"
149:    setenv PERLBREW_PATH "$PERLBREW_ROOT/bin"
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perlbrew

If latter on you need to change $PERLBREW_ROOT, you (and all other users who share the same $PERLBREW_ROOT will have to run this again to make it affective.

PERLBREW_ROOT

By default, perlbrew builds and installs perls into $ENV{HOME}/perl5/perlbrew directory. To use a different directory, set this environment variable in your bashrc to the directory before running perlbrew.

App::perlbrew

By default, perlbrew looks for the intialization file that exports PERLBREW_ROOT in ~/.perlbrew/init. In some cases (for instance, if your home directory is shared across multiple machines), you may wish to have several different perlbrew setting per-machine. If so, you can use the PERLBREW_HOME environment variable to tell perlbrew where to look for the initialization file

 # on machine a
 $ PERLBREW_HOME=~/.perlbrew-a PERLBREW_ROOT=~/perl5/perlbrew-a ./perl
+brew install

 # on machine b
 $ PERLBREW_HOME=~/.perlbrew-b PERLBREW_ROOT=~/perl5/perlbrew-b ./perl
+brew install
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If you specify PERLBREW_HOME, you will also need to specify both PERLBREW_HOME and PERLBREW_ROOT when you first install perlbrew. After that, you'll need to make sure PERLBREW_HOME is exported when you log in, before you source $PERLBREW_ROOT/etc/bashrc (or cshrc). Example .bashrc: