There's a contradiction in the question: If you can do
everything with react, you can certainly do
something that interferes with Liferay. That being
said, if you're aware of some specialties (like: You're potentially
sharing the page with different applications, potentially even the
exact same application) you should be good.
As a programmer, you don't have any influence over the users of the
portal, and how they compose their individual pages - thus your
applications should behave well and respect their own
(portal-provided) namespace instead of relying on anything global that
could easily clash with the same app twice on a page, or with another
app that happens to choose the same names in the global (DOM) namespace.
Also, check for the SPA framework that Liferay uses by default.
That being said: Yes, you can do everything. Depending on what you
actually do, and what effect you expect, you might need to limit
yourself (or ask a more specific question when you run into issues.
Asking for "everything" is a bit broad)
