If you need to customise the extranet login and forgotten password forms then follow the following approach (new for 10.2) should be used
Add two new reserved variable blocks with names below
When you first create a variable block with one of those names it will automatically be pre-loaded with an XSL that generates the default extranet login or password reset form. You can then edit these variable blocks in order to customise the appearance of the forms. If you need different variant across your site then different versions of the XSL can be used in different variable block schemes as necessary. If these variables do not exist, the form will be rendered exactly as it was before. Bear in mind the site setting 'allow retrieval of lost passwords' needs to be set for the second XSL and its related form to work
A previous approach using a customisable XML block named reserved__loginxml is still being supported but will be deprecated shortly, details of that are here.