will I lose purchases changing apple id

Yes, all AppleIDs are the same as the primary email address. But an AppleID is just that, an ID, which in turn is linked to an account with Apple.

If you change the primary email address, yes, you change the ID you will henceforth use as your AppleID - since these are always one and the same.

HOWEVER, as long as you change it at the web site I linked to, the ACCOUNT associated with that ID is unchanged, and all your purchases will now be linked to the new ID=primary email address, since all you have done is change the name you associate with that account.

If you don't change it there, but create a new AppleID with the new email address, your old purchases remain in a SEPARATE account, permanenlty linked to the old AppleID=old email address. Creating a wholly new AppleID also creates a wholly new account linked with that new ID.

You won't lose them but you will not be able to update them with your new ID. It is not possible to transfer ownership of apps between accounts.

If you go to

https://appleid.apple.com/

And simple change the primary email on your existing AppleID account, then nothing will change. As long as you simply edit the exisiting primary email at the web site above, your account remains unchanged and everything moves over to the new login primary email.

If you create an new AppleID with the new email address, then your current purchases will remain forever tied to the exisiting AppleID linked to your old email address.

Go to the website I mentioned above, login through the Manage portal with your current primary email and passwod. Beside your primary email address is an "edit" option, use it to change your primary email address, then click to have it verified. Respond to the verification email when you get it, and your exisitng AppleID will thenceforth use your new primary email address.

A long time ago, you were "allowed" to actually name your AppleID something other than your primary email address, you are right on that. I'm not sure when the rules changed to be that your AppleID had to be your primary email address, but it was awhile ago.

It is a bit confusing, but just think of the AppleID as just that, an identifier. The actual account it is linked to is a separate thing, stored internally by Apple, and all you have now done is merely changed the identifier linking to that (and still unchanged) account.

Just 37 hours later and that address <https://appleid.apple.com/> gives a page not found error.

You need to leave off the trailing / to allow the re-direction to work.

You can use either http or https and

appleid.apple.com is good - at least right now.

Also, when I login through the manage portal there is no 'edit' beside the primary email.

There is a way to edit my name and to add or edit my alternate email addresses, but again no way to edit my primary address.

http://support.apple.com/kb/HT5621

looks like good guidance/advice, but before I take the leap - is this tied only to the device? I ask as the reason I wish to change is that everyone in my household (multiple apple devices) has always used the same apple ID. I want to make sure that my ID is now separate without losing apps, features, ect...

Content and Apple IDs -

Content is forever tied to the Apple ID that bought it. Apple does not transfer content from one Apple ID to another. Apple does not merge Apple IDs. You will never be able to access your content bought with another Apple ID with a new Apple ID.

If i use apple id same icloud id, And anyone know my apple ID (they don't know my email), so they can change my apple id by change email to their email? That means i will lost my device? How can i move back my email ?

Nobody can change anything about your AppleID unless they know your password as well. Simply knowing your primaty email address does not give them enough information to actual alter your AppleID or its associated account.

If you really want to secure your AppleID, then (my opinion and whay I've done) Apple's two step verification system is something you may wish to set up - http://support.apple.com/kb/ht5570

In order to change anything once 2-step verification is set up, someone would have to know your AppleID (ie primary email address), your password, and they would have to be in possession of one of your trusted devices in order to receive the temporary 4-digit PIN required every time you wish to change any of your AppleID information (at https://appleid.apple.com).