MRN is a domain to request news. It uses OMM. RFA C++/Java supports OMM on 32 bits and 64 bits. Hence,you can request MRN on 32 or 64 bits platform via RFA C++/Java. However, we suggest you uses 64 bits platform rather than 32 bits because APIs new versions tend to support on 64-bit platform.
Actually, it depends on API that you are going to select rather than MRN itself. MRN is just a data structure to describe how Thomson Reuters delivers NEWS information, and the way that the receiver applicaion should handle it.
To check which API support 32-bit or 64-bit platforms, you need to refer to API Compatibility Matrix (now its version is 2.03 so far).
Normally, API Compativility Matrix can be found under a 'Documentation' tab of Elektron API or Thomson Reuters Enterprise Platform API.
Moreover, there are a bunch of Machine Readable News tutorials available in various Elektron/Thomson Reuters Realtime Platform APIs. You may select a 'Tutorial' tab (at the right side of the 'Documentation' tab for the additional MRN topic.