is there any way I can create like a package file that co-exist with my actual unity project on android? so that I can load stuff into project from this external package file?
Asset Bundles seem like the most obvious answer. They are a pro-only feature, though.
http://unity3d.com/support/documentation/Manual/Loading%20Resources%20at%20Runtime.html
note: created asset bundles would be in a folder "StreamingAssets" inside of your "Assets" folder in order to compile them correctly.
Hope that helps.
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