How to change the default set of programs in Xubuntu?

Question

linux

There are 60 machines running Xubuntu 14.04.3. The system was installed at different times, there are such instances that have been updated (successively 12.04, 14.04) already from version 10.04.
It is known that the set of default programs changes from release to release (for example, the gthumb viewer was changed to ristretto).
At the same time, I do not change my preferences in choosing programs, but delete unnecessary ones.
After removing the same ristretto, with further checking of dependencies
aptitude install -f
on about 20 machines, it suggests installing ristretto again.
I understand that these 20 machines were installed at the same time, from the same media.
Question:
where can I fix the default set of programs for this particular version of the distribution ?

Answer 1

sudo update-alternatives --config ....