Default Texture Platform/Format settings

So every texture has an option for iOS/Android to change the Size/Format/Compression.

I want to change this globally (i.e. rather than ticking override for all textures for Android, just change what the global default is for all textures)

Is this possible?

Thanks in advance

As of 2018.1 you can now specify default import settings for all kinds of assets using the Unity preset system:

In the Inspector Import Settings for each texture click on “Default”, and select the Size/Format/Compression.

Only if you want to override the default settings for a particular platform, you click on that platform and click the override checkbox, e.g. click on Android, and then and click the Override for Android checkbox.

Also, if you want to apply this to more than one texture, select all the textures and the default settings you set will apply to all of them.