On Android, how can I update files in the StreamingAssets folder?

My game have 100M asset bundles, I put the budle files into the StreamingAssets folder(I want to release my apk as one whole app, not the downloading when playing style), then I built my project into one apk file, then I installed the apk file to my device.

But how can I update my bundles when my game find one new update is available? The StreamingAssets folder on Android is read-only.

One solution is that: copy the bundles in the StreamingAssets folder to somewhere like the Android’s External Storage, then use bundles in the External Storage.
But this will increase my game size from 100M bundles to 200M.

So on Android when I install one apk, can I install some files meanwhile into somewhere writable?

Anyone can help me?
Thanks.

Because the StreamingAssets folder is read only you can not download updates to that folder as you say. A solution could be to just download update bundles to the external storage and on the start of your app check if there has been downloaded any updates. If there is, then load the downloaded bundles from the external storage. If not, then use the bundles in the StreamingAssets folder instead (as a default).

And as a reminder: keep in mind the 50MB filesize limit of Google Plays APK files. Anything over that size needs to be hosted in separate Expansion Files.