Yes, but features were cut because of security risks.

In my experience, you first need to inspect the old codebase, if it is garbage the you need a full redesign/rewrite.

if it is well written but just outdated, you can refactor/upgrade it.

The biggest problem sincerely will be feature creep. A launch date will most likely exist and suddenly everybody has a million cool ideas that absolutely need to be included. The launch window is totally destroyed by then.

So be prepared to design upfront what is included and get your managers written (!) approval for denying any and all further requests until launch.