The script must return the boolean value true to skip the backup.
Anything else including an error will be considered as false.
User interaction like display dialog is not allowed.
The custom condition has the lowest priority after time range (highest)
and network connection.
For example check for a specific IPv4 address;
set ipV4Address to IPv4 address of (system info)
if ipV4Address is "00:11:22:33:44:55" then
return true -- skip backup
else
return false -- run backup
end if
Note:
Be aware that the script is called from the local domain, not from the
currently active user. Calling the script in the home folder of a specific
user while the user is not logged in could cause unexpected behavior.