Is it possible to create interior within existing model?

I’m new to UE and so I was wondering: I recently bought the top down city from the market, which includes quite a few house models, but they all only have exterior.
Is it generally possible to take one of those models and modify it to create interior?
I mean, I’m sure you can, but what would be the way to go about it?

A bit of a general question but I’d like to know where to go from here.
Thanks in advance!

You could export the model you want to edit from the engine (right click > export) and import it into a 3D modelling program such as blender(free), 3ds max, maya, cinema 4d, etc…

In one of these programs you can modify the exterior model to also have an interior.

You would then need to uv unwrap and texture the interior so it doesn’t just show up as grey.

Then import it as a new asset back into UE4 again.