The official Trainzdev guide is here:
First the Engine specs:
Find the installed locomotive or download it Then open up Content Creator Plus and the asset details will be shown and you can change them. Find the enginespec tag and click the ... button. Then a 'KUIDBrowser' should come up. Choose the category enginespec and then find the 3F engine spec if you want a small tank loco, for larger ones use maybe a 5MT of Britannia spec. Then hit select, and do the same on the enginesound tag, except use the enginesound category. Use the 3cylinder obviously for a 3 cylinder loco, for a small 2 cyl tank loco it's best to use the 2 cylinder Stephenson included in the TC3 patch. For other locos, change it to the plain 2 cylinder sounds. Then, if you want to change the whistle, press the ... button in the hornsound tag and find the whistle you think would suit it. Then, using the list on the left hand side, click in the button that says 'Kuid-table'. Then simply click on the X sign next to the things displayed on the screen which show a KUID number instead of a name. Then click file, save then exit. When that's done, go back into CMP and commit the loco (Ctrl+M) and go for a drive in it!This method should work for any steam loco you want to convert.
The bogey will need the line
next the running number problem:
For the running numbers in TC3 and 2009 I think you may have to add the following line into the config.
The fonts-path tag points to the root directory folder of the model, The above is taken for the TC3 built in double chimney 9F. Below is an example from one of the Class 40 models
This will also need to be accompanied by
This value for this tag will need to adjust for the different amount of fonts used on the loco. To find out the number to put for this value look in the alpha numbers directory and if it has files named alphanumber_0a and alphanumber_0b then the value wants to be 2 due to 2 types of font in use. If its just alphanumber_0 then you want a value of 1. The fonts tag should already be present though on the models as this is required for alpha numbers to work in 2004 upwards.
Helpful information can be found here :