I installed berrybrew 1.22 on a vanilla win10 VM, installed and switched to Perl 5.10.1_32, then ran the new installer.

I have made some changes to the installer after the OP (you can get it here.

Here's the result of those actions:

C:\Program Files\Mono>echo %path%

C:\Program Files\Mono\bin\;C:\berrybrew\5.30.0_64\c\bin;C:\berrybrew\5
+.30.0_64\perl\bin;C:\berrybrew\5.30.0_64\perl\site\bin;C:\Windows\sys
+tem32;C:\Windows;C:\Windows\System32\Wbem;C:\Windows\System32\Windows
+PowerShell\v1.0\;C:\Program Files\Git\cmd;c:\Users\admin\Downloads\be
+rrybrew\berrybrew-1.22\bin;C:\Program Files (x86)\berrybrew\bin
[download]

So the new path gets installed *after* the old one. I will add some checks and throw a warning window to state that the old berrybrew will be disabled if they proceed, and I'll write a routine to automatically register any custom or virtual perls they may have had installed in the old version. If the user decides not to proceed, I'll just abort the setup.