It's very very simple. You just install one RA2 on your hard drive. Then you patch it. After that you just take copy and paste and rename the folder to, for example, Robot Arena 2 DSL-TC.
Now you have two RA2 folders but only first one has working registry markings but that doesn't matter the game at all.
Now you just install DSL-TC 2.0 mod into the Robot Arena 2 DSL-TC folder and that's it. Now you have duplicated the RA2 game to two different games.