Well, it can be done, with minimal changes.
You need to change local ip's and make ha ones as vip
Not a big thing
But, do keep in mind that all interfaces have to be created in the same order in both ha instances.
You will need some experience with the ha setup.
Many things can go wrong if you don't know what you are doing. (as is usually the case too)
I strongly suggest to setup a lab and experiment with ha setup. When you will feel confident, you can proceed with the real thing.
Doing such chores on a live system without prior experience will probably cause significant downtime.