Is it possible to to set a fixed NFC P2P RF speed for the Initiator? In NFC P2P communication, the RF speed of the LLCP connection is set by the Initiator. The possible speeds are 106kbit/s, 212kbit/s, 424kbit/s.

Android always choses the fastest possible speed.
For example I would like to set the speed to 212kbit/s.

Is it possible to set a fixed RF speed rate on Android side?
From a user perspective: No, that's not possible.

From a developer perspective: Maybe. Android does not directly provide an API that lets you choose a particular communication scheme/speed (the idea behind peer-to-peer mode is that the two devices automatically choose the best scheme that's suitable for both of them). Consequently, there is no way to do this without somehow modifying the operating system.

You could, for instance, create your customized OS and adapt the Android NFC stack to only use certain modes (for NXP's NFC stack, see the NFCIP-1 speeds enum in phNfcTypes.h:955 and the methods setP2pModes() (in NfcService.java:1083) setP2pInitiatorModes() (in NativeNfcManager.java:352) and setP2pTargetModes() (in NativeNfcManager.java:358). 

On a rooted device, there could be an even easier approach (i.e. one that does not require building the complete OS): While there is no public API for setting P2P modes, there is a hidden method setP2pModes() in NfcAdapter (in NfcAdapter.java:1373). However, in order to call that method, your app needs to have the WRITE_SECURE_SETTINGS permission (which is only granted to system apps).