Since you're a newcomer, it's not good that you already get annoyed because it's not easy to reskin some asset...
Some may not like someone to repaint ( that is ,modify) their work.
Keep in mind that the post you answer is two years old already
One of the ways you'd reskin an asset I've learned after using the sim is through photoshop, which is pretty expensive. I wonder if there are other ways of doing so.
Well, in truth it has the features from Photoshop circa 1995 but that is all you need for reskinning Trainz assets.
Now if you want something better, Humble Bundle has a Corel bundle and the $1 tier has Paintshop Pro 2023 included. Click on the 2 item bundle filter to see the $1 tier offer.