How to do change model on simulation by "lsim" ?

I want to change model on simulation by "lsim". Because I want simulate the condition that during operation Big Network model (power system .etc)having node 30, Nodes increase 31 or 32. Using next code, I achieve my target.It is image, so next code is not work.If sys.C is Identity matrix, y_before is stateof system.Using x0 of "lsim", changing system simulate complete?(may be). Please tell me more good idea. Best Regards.

 y_before = lsim(sys_orinal,u(1:end/2),time(1:end/2),[0,0]);
 y_after  = lsim(sys_change,u(end/2+1:end),time(end/2+1:end),[y_before(end,:),0]);
 y = [ y_before; y_after]; 
%{
where
   sys_original : Original sysmtem
   sys_change : Original system + Add Node
   time ; simulation time
   u : input signal (input only original node)
%}