It's possible, but I think it entirely depends on the scope of your investigation. If you want to write about intelligence policy or analysis, you're likely to have an easier time than if you want to write about intelligence operations. But it's certainly not impossible to do either, given how much has been written about the CIA in the Cold War. The challenge will be getting access to interesting primary source material.

The CIA themselves publish a lot of material via the Center for the Study of Intelligence, including declassified documents of historical interest and declassified articles from Studies in Intelligence, their in-house journal.

You can also search material previously released in response to Freedom of Information Act requests. But actually, the best advice I could give would be to familiarise yourself with FOIA and consider submitting your own requests, bearing in mind that it may take a long time for you to receive a response, let alone any documents — and that it's possible or even likely that your request may be denied.

A cursory search of their FOIA releases for 'Berlin' turns up a scattering of documents; mostly policy documents and internal reports around the Berlin Crisis and the building of the Wall. But a wider search of their site also turns up this account of an academic conference on intelligence operations in Berlin from 1945-1961 and this accompanying book, published by the CIA, which includes some interesting primary source material.

In terms of wider historiography, I'm still yet to find an up-to-date, comprehensive scholarly history of the CIA. Bear in mind that intelligence history is still a relatively new field, and the CIA is seriously (though unsurprisingly) cagey about its operational archives. They do, however, offer a suggested reading list — make of that what you will.

As a starting point, though, I'd say you should check out Richard Aldrich's The Hidden Hand: Britain, America and Cold War Secret Intelligence and Christopher Andrew's For the President's Eyes Only: Secret Intelligence and the American Presidency from Washington to Bush. It's more investigative journalism than scholarly study, but I'd also recommend Tim Weiner's Legacy of Ashes, which is probably the best single-volume history I've encountered.

Also: I haven't read it (or even heard of it until I was googling just now) but it turns out that the CIA's station chief in Berlin co-wrote a memoir with his opposite number, the KGB's Berlin resident, so that's probably something you want to check out too — Battleground Berlin: CIA Vs. KGB in the Cold War.

Hope that helps; would be really interested in hearing more about what you want to investigate!