Do you mean through code - or through the admin interface.

I would certainly encourage adding properties to page types in code for CMS7.

There's an excellent article on how to do this by Alexander Haneng: http://world.episerver.com/Blogs/Alexander-Haneng/Dates/2012/7/How-to-define-properties-in-EPiServer-7---A-quick-reference/

Unfortunately, however, it does not provide an example of how to do this if the episerver builtin property has a hyphenated name.  As is the case with EPSUBSCRIBE-EXCLUDE.  In code this fails.  I assume because the hypen is considered as an operator and illegal in a variable name.  My colleague posted to Alexander's post asking how this might be achieved, but so far there has been no response.  Giving it another push here - so I trust this is the same question that you are asking.

PK