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.
I want to exclude pages from a parent page that is subscribed to.
I have set the EPSUBSCRIBE for the pages that you can subscribe to.
How can i set the property EPSUBSCRIBE-EXCLUDE in my episerver 7 pagetype?
I would also have it to default to true.
Thanks for any help.