I know that it is possible to add 18.04 repos in 20.04 (by manually adding a keyserver and adding a .list file in sources.list.d) but (if all the dependencies are corrected) is it safe to add them? Will it break your computer/Ubuntu installation? Thanks!
Running Ubuntu 20.04. Dual Boot with Windows 10.
Technically it can be added but I would not recommend it. In case you are installing some application and its dependencies going to break existing other application in systems. it can break dependency tree and will end up in mess. Here scenario depends on application to application and its dependencies.
I would suggest installing any other applications (which are not available through Ubuntu version's official repos or any other third party repo), via deb packages or compiling source code.
