How do I debrand my T715a?

Hello everyone, I just got my hands on a SE T715a but unfortunately the provider (Fido, Canada) has locked all kinds of stupid things, like the ability to use MP3s as ringtones, or even delete the crappy game demos! :(
I'd like to get rid of these restrictions without changing anything else (or unlocking the phone), if possible. Now I have a customize_upgrade.xml file someone else made for that phone and provider that's supposed to remove the file restrictions. The problem is I can't seem to upload it with a2uploader because of something about being unable to read/write CID53 red. I'm new to this whole debranding/unlocking thing, so I don't quite fully understand what I should be doing here. Can anyone point me in the right direction?

Thanks! :)