Yes..it safe. We don't post or suggest anything that unsafe . But rules of the thumb "Flash At Your Own Risk"Is the custom ICS safe to use with Australia 3g networks? Sorry just new to this.
Like Mickeymic, warranty voided as he running firmware that not meant for his country.(You can revert back for warranty purpose,if any)
If you going for custom, choose "EU 3G Xoom (umts_everest / MZ601)" to have working 3G and it will work for Australia.
Gd luck..choice is yours