WORD WRAP ON

Step 1	- Open trinity2.wtd file via OpenIV with edit mode ON
Step 2	- Select the livery you want to replace (basically the one you don't want)
Step 3	- Import your desired livery into the slot. All the settings should be automatically applied. If not, it should be DXT5 and 9 Mipmaps.
Step 4 	- Save the .wtd file and test in-game

You have up to four slots available in-game. By default, slot one is occupied by a blank texture to let it spawn without any liveries. You can replace that slot as well.

Similarily, if you don't want any liveries at all you can just delete all of them (except the blank one) from .wtd and save the file.

For a quick test, open up trinity2.wft in OpenIV. Though it will only show the livery in slot one. You can temporaliy replace the blank one for your own choice then revert later.