Sorry, I wasn't clear enough about the texture= thing. Try this:
Your new texture folder should be named texture.whatever so that FS knows this a texture for the aircraft. Now put the last part (whatever) on the texture= line, so you end up with texture=whatever.
If this is already the case, make sure the ui_variation is something different than the others. If it is the same as one, FS will use the first one it comes to and disregard the latter.
If THIS doesn't work, try looking at the files in the new folder. They must have the exact same names as the ones in the other folders, otherwise it won't work.
At this juncture, you might also want to find a program named Imagetool, found in the Gmax section of your FS (if you have FS2002 Pro), or I think you can download it from the SDK section on Microsoft's site, here:
http://www.microsoft.com/games/flightsimulator/fs2002_downloads_sdk.aspThese are great things to have anyway, so take a minute to read over the descriptions and see what you might want.
The reason to have Imagetool is that some FS textures are in a format inacessible without being reformatted, and Imagetool allows you to do that, and then change them back again after your done painting. If your aircraft shows up as a matte gray when you try to load it, this is most likely what you need to get.