I am a left-handed user who switches the buttons on my mouse so that the primary mouse button is on the right. When remotely accessing a shared system, the mouse button (left or right) not the button assignment (primary or secondary) seems to be passed through to the remote so I find myself having to use the "wrong" mouse button on the remote. (I imagine this would have to be a per-remote setting since I might be using RDM to access a system configured to my preferences and double reversing would just break things again.)
I've used Royal TS for a while and their response to this request was kind of lame so I'm sure it will never be fixed there. If Remote Desktop Manager supported my mouse settings, I'd switch in a heartbeat.
I realize that the remote desktop protocol may carry button numbers, not functions, but it seems you should be able to intercept a mouse click within the child window and swap the numbers before sending the event to the remote so the desired assignment would be achieved.
Unfortunately we both use the Microsoft RDP ActiveX. We could check if this is possible to do that with FreeRDP but it's not a simple feature.