Absolutely! Copy your existing folder (ie Su-33) and rename it to whatever you want (ie Su-35). Now your new Su-35 folder will be identical to the Su-33 you've copied it from. Make sure you rename the Su-33.ini to Su-35.ini otherwise it will not show in the aircraft list in-game.
I'll give you instructions shortly, but I'm at work at the moment and the instructions are a little tricky and will require the use of a hex editor. If you haven't used one before, never fear, what you'll be using it for will be VERY straight forward.
I have noticed one thing about copying and renaming aircraft though. I have about 4 different variants of the Su-27 family with canards in my install, and in after action reports, it displays the file name, not the aircraft name. For example, one of my Su-35s uses the filename "Su-26". In the AAR you'll see "1 Su-26 was damaged" instead of "1 Su-35M was damaged."