Any modifications of the sprite would have to be released publicly, which just means the modified sprite also needs to be under the CC-BY-SA 3.0 and be available in a modifiable format like PNG. But just rescaling doesn't modify the sprite substantially, I don't think it is necessary to add special credits for that.

As for crediting me, it's nice of you to mention that, but the work on this sprite is entirely b_o's - I just commissioned it. Mentioning or linking to the game I commissioned the sprite for (Wyrmsun - http://store.steampowered.com/app/370070/Wyrmsun/) would be nice but isn't required.

MedicineStorm explained it perfectly :)

Unfortunately it is not something I can change. These were the two particular licenses (GPLv2 and CC-BY-SA 3.0) that the artist agreed to.

Hello MedicineStorm,

You are absolutely right in wanting to sure of permission before posting it here. The sound data is contained in 7KAA's package within the \data\resource\ folder, in the a_wave1.res and a_wave2.res files.

The source package's readme reads:

"This is a GPL release of the Seven Kingdoms: Ancient Adversaries thanks to
Enlight Software which granted the ability to license the game under a
free and open source license in 2009. See the file "COPYING" for the
details of the license.

[...]

What is missing from the open source version of the game
---------
* The original game music. The music is provided by 7kfans, but separately
  from the source tree. It is not under the GPL license, but it is free to
  download and use with 7KAA.
* The original game intro video. Support may be restored in future releases.
* Any other content from original game CDs, game manual, including the version
  2.12b game binary or older. This also includes the I*Magic Online service."

Well, the sounds are included in the open-source package (in the exact same manner as the graphics), so it seems clear to me that the license also applies to those sounds.