Just sharing a way to change outfits, for anyone who is interested.

Look for ESam.ukx in the animations folder, back it up in case of error, and open it with Notepad++(regular notepad or other text editing programs might work, but I did not test).

Look for:

-samAMesh

-samBMesh

-SamCMesh

and just switch the A, B and C alphabets with one another as you like.

The A mesh is the outfit worn in the training mission and most missions. B mesh is the "ninja" outfit. As for the C mesh, I'm not really sure what it actually looks like but I'm guessing it's the one with elbow pads.

So basically, if you want the "ninja" outfit for missions that use the A outfit for example, just change:

samAMesh > samBMesh

and

samBMesh > samAMesh

This will also mean that missions using the B outfit will show the A outfit. So you'll need to switch the alphabets again if you want to retain the same appearance. If you use any other alphabet, I believe Sam becomes invisible as the mesh doesn't load. Also, using the same alphabet for two meshes at once resulted in a crash for me.

That's all :). Apologies in advance for any problems with this post and if this doesn't work or causes problems. However, it works fine for me. Also, thanks GOG for this great game!