You can have more than one version of M&B installed at the same time, you just have to install them to different folders.
For instance, I have .808, .903. and .953 all installed on my computer right now. They are installed in:
D:\Games\Mount&Blade808
D:\Games\Mount&Blade903
D:\Games\Mount&Blade950
I just have 3 different shortcuts that point to the mount&blade.exe in each of the folders. That way you can still play the latest version of Native, and also mods from older versions. Just make sure to install each mod to the correct version.