Army-Navy Guy

Humm. I think I got screwed on my right knee replacement %. (30% right after replacement, 10% left that is as bad as the right pre replacement.) So the question is what are you ratted at for your PTSD? Are you a 100% scheduler P & T or 100% P & T UI. Depending on what your PTSD is you should be close  to getting a 100% scheduler rating that doesn't have the restriction of a UI. The new ratting you are seeking should put you over to a 100% scheduler.

Welcome to Hadit.com
Can you list what you are ratted for and the percentages. It will help us point you in the right direction. You are not correct in that adding to your 100% P & T will not get you any more $$$. You may qualify for SMC and other benefits depending on how the percentages are. 
 

"Pain" may be included already in your original rating.  So, you cant be rated for the same syptoms twice.  Yes I am rated for secondary conditions.  
You need a nexus where the doc states your (new condition that you seek) is at least as likely as not related to (your currently service connected condition).  Of course, you need a diagnosis, for both by a doctor.  You already have a diagnosis for your sc condition, or you would not be sc for it.