When rebuilding mozc with Mozc UT Dictionary, it may be better to build in docker container because you don't want install unused IM development packages.
In beforehand, download latest Mozc UT dictionary here.
osdn.net
In a debian/sid container, you need to do it:
# apt install -y devscripts
# (enable deb-src, modify /etc/apt/sources.list.d/debian.sources)
# apt source mozc
# cat mozcdic-ut-20221230/mozcdic-ut-20221230.txt >> mozc-2.28.4715.102+dfsg/src/data/dictionary_oss/dictionary00.txt
# cd mozc-2.28.4715.102+dfsg/
# (edit debian/changelog such as 2.28.4715.102+dfsg-2.2.1 )
# debuild -us -uc -nc
After that, you can install
% sudo apt install ./emacs-mozc_2.28.4715.102+dfsg-2.2.1_amd64.deb ./emacs-mozc-bin_2.28.4715.102+dfsg-2.2.1_amd64.deb ./fcitx-mozc-data_2.28.4715.102+dfsg-2.2.1_all.deb ./fcitx5-mozc_2.28.4715.102+dfsg-2.2.1_amd64.deb ./ibus-mozc_2.28.4715.102+dfsg-2.2.1_amd64.deb ./mozc-data_2.28.4715.102+dfsg-2.2.1_all.deb ./mozc-server_2.28.4715.102+dfsg-2.2.1_amd64.deb ./mozc-utils-gui_2.28.4715.102+dfsg-2.2.1_amd64.deb
Then, you can use own build binaries.
% dpkg -l |\grep mozc
ii emacs-mozc 2.28.4715.102+dfsg-2.2.1 amd64 Mozc for Emacs
ii emacs-mozc-bin 2.28.4715.102+dfsg-2.2.1 amd64 Helper module for emacs-mozc
ii fcitx-mozc-data 2.28.4715.102+dfsg-2.2.1 all Mozc input method - data files for fcitx
ii fcitx5-mozc:amd64 2.28.4715.102+dfsg-2.2.1 amd64 Mozc engine for fcitx5 - Client of the Mozc input method
ii ibus-mozc 2.28.4715.102+dfsg-2.2.1 amd64 Mozc engine for IBus - Client of the Mozc input method
ii mozc-data 2.28.4715.102+dfsg-2.2.1 all Mozc input method - data files
ii mozc-server 2.28.4715.102+dfsg-2.2.1 amd64 Server of the Mozc input method
ii mozc-utils-gui 2.28.4715.102+dfsg-2.2.1 amd64 GUI utilities of the Mozc input method