Change text in Verification Email

Hi,

What would be the function code to change out the text that currently reads:

Your account with ________ needs to be verified before you can access your purchase history. Click here to verify your account.

Link missing? Visit the following URL: https://_______

WHAT I NEED:
This message is so vague that people have no idea why they are receiving it after they’ve already gotten a paypal email, a wordpress email and a thank you for signing up email.

SO:

1 – Do I assume correctly that this email is only being sent if the person already signed up in the past and now is coming back with a different username but the same email?

2 – If that is so then I’d like to inform them of that. Something like “We’ve noticed that you’ve tried signing up to ____ with a new email account. We just need to verify this with your username. CLICK HERE to verify your account.

3 – I assume it’s going to be some form of add_filter but not sure what the access info would be to write it up.

Thanks in advance for supplying the function code for this!