The simple answer to this question is No, or more accurately you probably shouldn't.
I've seen many requests sent from customers and internal engineers on "How do you customise the Request Access Email that SharePoint sends out?". I decided to have a look at this and found the request access email that is sent out is built inside the SharePoint code which means there is no way for the you (a customer) or us (Microsoft Services) to change it for you.
In particular the option that caused me to look at this was how to send the Email out using a Preferred Display Name rather than the users Domain\UserName.
The property we use for the user is the WindowsIdentity.Name Property, which is the logon name in the form DOMAIN\USERNAME.http://msdn2.microsoft.com/en-us/library/system.security.principal.windowsidentity.name(VS.80).aspx
The WindowsIdentity.Name is also what is shown on the reqacc.aspx page when the user is redirected to this page. “You are currently signed in as: (WindowsIdentity.Name)”
There is one way to workaround this and that is to build a custom reqacc.aspx page and not use our Out of the Box page. Since the page is stored in _layouts you should review KB944105 before deciding on this option.
944105 How to customize application pages in the Layouts folder in SharePoint Server 2007 and in Windows SharePoint Services 3.0http://support.microsoft.com/default.aspx?scid=kb;EN-US;944105