The Monitor

I'm at the beginning of learning the arm architecture and I understand this question might have been answered somewhere in the A.R.M document. But I got confused with this particular question and some short answer would be helpful before digging into that thousand page document further.

Suppose I want to implement my own OS (and some standard firmware which goes right after the rom code, like for example UEFI). And I want to make its (their) Secure part(s) too. Can I implement the Monitor? Again I've read not much (to be honest), but the documentation from vendors looks cryptic somewhat on this. For example TRM on TI's Sitara AM3358 SoC in th description of its rom code and its work only states that it starts in Secure (private) mode and then switches into the Public mode. Ok, but what if I want to implement Monitor code with my UEFI/OS? with the present rom code my firmware would be loaded by it and it ends up being in the Non-secure state. The only thing I can do is to issue SMC for some whether not documented or just rudimentary implemented "services" from the monitor mode. But what If I want to take the responsibility of giving users this Secure/NonSecure splitting stuff by my own with my implemetation of this? Or this is impossible for third parties? If that is possible, how do I include my code into that supposed secured path, chain? I mean how do I replace the existing monitor with my own on a security extension capable arm SoC? Should I sign my code, send it for review or else? Maybe there are some answers to this or a direction (not offensive xD) to where should I look for getting the answers.

Thanks! (sorry for the poor english)