Welcome to the Bunnings Workshop community. It's wonderful to have you join us, and thank you for sharing your question about cutting Colorbond fencing posts.
I'm so sorry but the store does not cut any kind of metal posts. The ideal cutter would be to use a grinder with a metal cutting disk. However, if you don't have a grinder you can also use a hacksaw to cut the metal post. Please make sure to always wear gloves and eye protection when cutting metal.
It sounds like you are putting in new fences. Any updates you can provide would be highly appreciated.
If you have any other questions we can help with, please let us know.