I think you are right, perhaps with the "export" the variable affects all the mldonkey's user activities (root and other users shouldn't be affected), but this is only a supposition.
I have also read about another way to apply(for sure) LD_LIBRARY_PATH only with the mlnet program
Remember that if you close the current shell and you didn't update ~/.bashrc, you'll have to repeat step 6 when you intend to run prog again. On the other hand, if you want to make the new LD_LIBRARY_PATH variable effective for prog only without affecting subsequent programs started from this shell, then skip step 6 and start prog like this instead:
$ LD_LIBRARY_PATH=~/lib:$LD_LIBRARY_PATH ./prog arguments ...
$ LD_LIBRARY_PATH=/new_libs_path:$LD_LIBRARY_PATH ./mldonkey_path/mlnet (arguments?)
Naturally this solution needs further testing.
I'm very happy to see there are 2 different ways to make my core to work properly
for sure: chroot and LD_LIBRARY .
@Togeis: if you like you could write a bunch of chroots's tips
Thanks for your precious feedback, I'll update my main posts in few days with your reports.