Hey there,
Yes, Spine allows you to use slots and attachments to swap out things such as body parts, clothes, weapons etc for others at runtime, that's actually one of it's main strengths.
For exporting and compiling, Spine is supported on all platforms and my extension uses native GML functions so also works on all platforms that it supports.
However, as you say you are using GMS 1.4, you should be aware of a few things:
- iOS and Android exports will no longer be accepted onto the App Stores due to store requirements changing since 1.4 support and updates were ended. You should still be able to test locally on your own devices however.
- GMS 1.4 only supports an older version of Spine, so you would not be able to use the latest version of Spine to create your animations.
I believe the most recent version supported by GMS 1.4 is Spine v3.4.02. - GMS 1.4 has been sunsetted for a long time now so if you want to publish your game onto Google Play or the App Store then you should look into purchasing GMS2.
Hope that helps!