Simple mod to built-in function

["Richard Harper" <rdharper@xxxx>]

Hi;
 
How do I modify, for instance, MFI to change period 
from 14 to X.   
 
I got that one has to add the modification 
before  
//--Indicator-End-- -- do not remove 
this line.
 
But I do not seem to have any luck by setting 
MFI(x);  
 
Trying to make my chart match my optimized 
settings.
 
Thanks,
Richard