In the project I am working, we are using Freebsd and we are creating our software packages for it. Now we are planning to change distribution to Centos and rpm for packet manager. Since our codes are not platform independent, we have to make many change on it. Also we will continue to use freebsd until migration is completed. What is the best git usage way for this type of migration. Should we use a new branch or a new repository? 
What should be done on git while migrating new distribution and packet manager?
git;migration;software distribution
The projects under Git, will you need to redesign the fundamental architecture because of this migration? If a project changes fundamentally in such a way that the new iteration is like a completely new project, then it makes sense to create a new Git repository for it.If there won't be a fundamental redesign, only relatively superficial modifications, for example porting tools, shell scripts, Makefiles from BSD to GNU, but the architecture / framework /skeleton of the project staying basically the same, then it probably makes more sense to create a branch instead.