Thank you for your assistance.
Quick question, when using Spine for Unity, is it possible under the license to
maintain the source code in the provided Spine package if we want to improve
performance?
Handling of Spine source code for Unity version
You can make changes to the Spine Runtimes without special licensing. The Spine Runtimes License Agreement applies:
http://esotericsoftware.com/spine-runtimes-license
Also see Section 2 of the Spine Editor License Agreement:
http://esotericsoftware.com/spine-editor-license#s2