Clarify rejection of register writes

Author: glopesdev

BinaryProtocol-8bit.md

@@ -217,7 +217,11 @@ The [`Error`](#error-flag-1-bit) flag in the [`MessageType`](#messagetype-1-byte
 
 Requests which require prior configuration of multiple registers (e.g. starting a pulse train, moving a motor), or requests which are invalid due to particular combinations of other register values, SHOULD NOT be handled by sending an error reply.
 
-Instead, such cases MAY be handled by sending an event message from a different register. Alternatively, an allowed value MAY be inferred and set, in which case the reply to the request MUST contain the actual register value which was set.
+Instead, such cases MAY be handled by sending an event message from a different register. Alternatively, an allowed value MAY be set by the Device, in which case the reply to the request MUST contain the actual register value which was set.
+
+> [!NOTE]
+>
+> A Device MAY reject a change to the register value. In this case, a reply to the write request MUST still be sent, containing the current register value.
 
 If an event message is sent from a register in response to a request sent to a different register, the documentation for the event register SHOULD clearly indicate which cases will raise the event, including specific combinations of values leading to error.