For example, imagine we have two packages: banana.deb and banana-common.deb. Inside banana.deb, we have some file banana.data, that is quite big and changes rarely. Both packages are currently at version 0.0.1, and banana depends on banana-common.
Now, because we want to reduce banana.deb size, we want to move that banana.data file into banana-common package. If I just do that (updating both versions to 0.0.2 and try to install with dpkg -i, I see the following:
$ sudo dpkg -i banana-common.deb banana.deb
...
dpkg: error processing banana-common.deb (--install):
trying to overwrite '/usr/local/banana/banana.data', which is also in package banana 0.0.1
How can I fix it without removing the package first?