About half of my subscribers use different emails in their DNN account and their paypal account. People just don't use their Paypal login for other purposes. Is it possible to use the different emails?

In the new version of this module subscribers can use different emails for their DNN account and PayPal account

Does you module display the paypal url in the browser address bar? i.e. is it easily manipulated by users to change price etc.?

When you navigate your mouse on Subscription button, you won't see paypal url in the browser's status or address bar. When you click on Subscription button you'll be redirected to the paypal page, in the address bar will be url with parameters (including cost of the service). Even if you try to manipulate with this cost, you won't get necessary role over our module and correspondingly you won't get a subscription service. Your clients will have to pay the exact sum that you set in the module settings.

How can I change the standard subscription button to my own?

You should open ViewSubscription.ascx file that is located here -

<root>/DesktopModules/CodingStaff.Subscriptions/

find the following code:

<asp:ImageButton runat="server" ID="btnSubscribe" OnClick="btnSubscribe_Click"
        ImageUrl="https://www.paypal.com/en_US/i/btn/btn_subscribe_LG.gif" />

change the path to the image from https://www.paypal.com/en_US/i/btn/btn_subscribe_LG.gif to another

and save file.