It is illegal to trap possums and release them away from your property.
Possums are highly territorial so relocating them elsewhere will only result in the released animal being attacked by possums already in the area.
This method is considered inhumane. It is very stressful for the animal and will result in the death of the possum regardless of where you release it. It may also spread disease if the animal is sick.
If you have released a possum elsewhere in the past, it may look like it has returned. This is highly unlikely. The possum you relocated will have died under very stressful circumstances.
Possums are part of the natural and urban environment and are territorial. Relocating a possum will not solve your problem. It simply means that a possum territory will be vacant for only a short period of time before another possum arrives.
Please see these documents about how to manage possums in your environment: