How to set property parameters from COS?

You may define properties by writing to ##class(%Dictionary.PropertyDefinition)
as part of a ##class(%Dictionary.ClassDefinition) 
http://docs.intersystems.com/latest/csp/documatic/%25CSP.Documatic.cls?P...

Parameters is then defined as array of %CacheString;  

And you set it just as any other array.  [SetAt() ..... ]

and then compile the class to use that property inside the class
 
This is nothing you may do on the fly.