I want to just quickly test the patch in this bug report to gtk3-engines-oxygen so it can go upstream. I could test it either temporarily or permanently; I would just like to do it. I currently have the package installed. So far, I've tried:

$ mkdir /tmp/o # keep everything self-contained
$ cd /tmp/o
$ apt-get source gtk3-engines-oxygen
$ cd oxygen-gtk3-1.3.5/
$ patch -p1 < /path/to/patchfile
$ dpkg-source --commit # to make debuild happy
(name 'layout'; just save the default; this is a test)
$ debuild -us -uc # bypass signature checks
$ sudo debi ../oxygen-gtk3_1.3.5-0ubuntu1_amd64.changes

According to some people on #ubuntu-packaging, this is what I have to do. It's this last step that's the problem; I'm getting

(Reading database ... 503333 files and directories currently installed.)
Preparing to unpack gtk3-engines-oxygen_1.3.5-0ubuntu1_amd64.deb ...
Unpacking gtk3-engines-oxygen:amd64 (1.3.5-0ubuntu1) over (1.3.5-0ubuntu1) ...
dpkg: error processing archive gtk3-engines-oxygen_1.3.5-0ubuntu1_amd64.deb (--install):
 trying to overwrite shared '/usr/share/doc/gtk3-engines-oxygen/changelog.Debian.gz', which is different from other instances of package gtk3-engines-oxygen:amd64
Errors were encountered while processing:
 gtk3-engines-oxygen_1.3.5-0ubuntu1_amd64.deb
debi: debpkg -i failed

What's going on? How do I fix it? Or am I doing this completely wrong (and ergo so are they)?

I'm using Kubuntu 14.04 amd64. Thanks.