Dynamics CRM 2011, 2013 and 2015.
If I customize the task entity, CRM allows me to create a new form for that entity. Likewise, I can create new forms for the Phone Call, Email, Letter, Service Activity and even Campaign Response activities.
So, why on earth is the "new form" button deliberately hidden when customizing the Appointment activity entity?!? Why can't I have multiple Appointment forms when I can do so for all other activity types?
Unfortunately given the advanced functionality built around activity, I believe Microsoft has locked down this ability. You can modify the existing forms but you cannot create new ones.
Same sittuation here.
It is not possible to create new forms for appointment entity but you can edit the existing ones.
Please refer the following thread.