Is it possible to replace Zorin with Deepin OS without installing it from scratch? I need to have the existing applications I installed on Zorin but want to have the interface of Zorin. Is it possible?
If I understand your question correctly, no, you cannot install Deepin OS on top of Zorin OS keeping the essentials of Zorin OS while using it on Deepin OS.
Zorin Lite uses XFCE desktop Environment and Zorin Core uses Gnome Desktop Environment.
Deepin OS uses Deepin Desktop which is based on QT and is more similar to a gnome-like KDE. You would not be able to use Zorin Themes on Deepin, even if you installed them over.
You could install the Desktop Environment you are used to with Zorin on Deepin, then install the themes and apps you are used to. It is a bit of work.
You could “install alongside” and have two separate OS’s on yoru machine and switch back and forth as needed.