If I recall correctly, there are some models which can be reskinned, but I don't think that capability is in surveyor, but rather in the content management section. I have purchased T12, but have been too busy in my day job to have the time to install it, so I can't tell you at the moment where exactly to look.
One thing to know, if you don't already: skinning (or reskinning) a model is a skill which is done best by those who have at least a passing acquaintance with graphics editing software. Nearly all models in trainz can be thought of as pictures pasted to boxes, with the pictures and boxes being more or less sophisticated. Reskinning is changing the pictures on the box, and to change the picture, you need to know how to use the software. GIMP (available as a free download from
www.GIMP.org), the GNU Image Manipulation program, can be used to make the images needed, or change existing ones to fit your requirements, but it's not a simple program, and it will take time and practice to learn to do it well.
However, although I believe it is intended for an earlier version of Trainz, there is a resource which may give you an overview of what's involved in reskinning at
<http://www.gaurc.us/files/info/ReskinningForDummies.pdf>
Good luck.
ns
