I suppose you could convert the DDS files to BMP's and use the color replacement tool of whatever you're painting with to switch the colors then make the new DDS files and put it back into the sim but I wouldn't expect clean lines. I think you would have fair results at best. If you decide to try it, copy the plane you want to replace the colors on then make your changes and install it as a new plane. That way if it doesn't work out you haven't lost anything. Ideally the best way to do it is to make a new paint.
There are tons of repainting instructions out there. A few years ago when I was a puppy painter the best one I found that worked for me was some YouTube videos from Mr Turbine777. He has a 22 video series that covers most everything you need to know and how to do it. Here's a link to the first one in the series: https://youtu.be/ztyJlKDbdwA I've also gotten a lot of help and ideas by searching the topics in this forum.
Unfortunately, I don't have the Flysimware Lear 35A so I'm unable to assist you repainting it.