Hi. I've gotten the Tgatool a while back, but hadn't had to use it until I got Trainz Railroad Simulator 2006, since it uses .texture files. The tga tool can open them and make them .tga files, but I'd like the program to convert them back to .textuure files when finished. I know how tgatool was mainly developed for MSTS, but I hope it will continue to give more support for Trainz. So I hope the next version will be able to export textures in Trainz's format.

I have never worked with Trainz myself.
I was approached a long time ago by someone who did and his situation was, if I remember, that Trainz itself comes with tools to create texture files from Targa. What he needed was some way to extract the texture files as targa so they could be edited.

Extracting is a lot more straightforward than inserting so it would be difficult to write code to convert the targa back. And a bit pointless if Trainz still comes with the tools to do it.
It is actually similar with MS Train Simulator. I can convert ACE to targa but to do the reverse I just utilise the MS MakeAce tool