Membership Buddypress Registration

Several questions regarding integration with buddypress and membership plugin

1. FIELD VALIDATION
How do I intercept the field validation during user registration? I would normally use

function sacbw_validate_user_registration()
{
	global $bp;
$bp->signup->errors['some_field'];
}
add_filter ('bp_signup_validate','myfunction')

the filter works but there are no errors in the $bp->signup variable even though I deliberately make error. Be that as it may, the plugin does pickup the errors because it displays them on the registration page.

I just want to know where it is validating the fields. Is there a hook for this validation?
Thanks.

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2. CUSTOM BUDDYPRESS REGISTRATION PAGE

Membership overrides the original buddypress registration page and adds its own. I want to customize this new registration page without hacking the plugin.

How do I do that?