Generally, apps should work on newer versions of the OS. Occasionally bugs do show up, though, and the older your version of the OS is, the more likely there would be changes.
In theory though, since Python's so high-level, any problems would be a part of the converter app itself instead of your code (I would think, I haven't done much with Python so I can't be positive). I'd check out the support forums or ask the developers of the converter apps to see if there's any issues. I'd imagine that if anything, you'd face the opposite problem...the apps might convert for the newer versions fine, but be too new for your version of the OS.