A question about using example game projects

My compnay is currently working on VR project and I have a question to ask about
using example game projects created by Epic’s developers and artists

Can we modify example game projects and utilize the source for commercial
use that is made with different video compositing tool (Ex: aftereffect,
cinema4d) ?

I don’t think I understand your proposal (sorry - I’m a lawyer not a developer). Could you provide more details of what you intend to do?

We are trying to use example game project’s source that is uploaded on the website for free. (For study use)
I want to know that we can use it for commercial use.
We are not just going to copy and paste the source. We will going to modify them.

Do we have to pay for loyalty for that?

You are free to use the free Learning tab content/examples for evaluation and for commercial use with UE4. Whether a royalty is owed depends on the nature of the commercial use.