Skyrim is not an open source game so you cannot touch the executable and only Bethesda is able to modify and compile it for the 64bits.
It is a game for console and so it is 32bits. When a console game is "ported" to PC, it needs some few adjustments but mainly the code is the same. Making a 64bits version requires to compile the source to 64bits and several things change. It is not enough to do a build64. It needs a specific version for the PC. As you can see here (
http://www.statisticbrain.com/skyrim-the-elder-scrolls-v-statistics/), the market for the game is mainly for the console while only 14% is "reserved" to PC users. So in general there is not so much interest for Bethesda to work on a specific 64bits version for the PC. In addition, he is working on the TES VI, so i do not think you will see a Skyrim 64bits (never).
Skyrim Reloaded - SKGE is a multipatch dll plugin that, with the help of SKSE, is able to patch several parts of the game (like Oblivion Reloaded - OBGE for Oblivion). I am the only active developer at today (sometimes i find Ethatron here who gives me some tips) because the other developers have left. Also i have not so free time for modding but i am bringing ahead the work a bit at a time.
SR is able to inject custom shaders into the Creation Engine hooking directly the game engine (so the power is that SR doesnt work on the directx but directly on the Skyrim's code, this makes it a "real extension" of the game with full compatibility, high performance and a total integration like a Bethesda patch).
Anyway no sources exist, so lot of time is required to understand how to patch. But i am a 20 years developer and i am quite good to develop and to reverse the code but i spend a lot of time when i have to modify/create a shader because i am not a shaders developer, so i need to look for a solution on internet and to try to apply it. The shader genius is Ethatron
but is seems very busy