There might be more efficient ways to do this
but… one is to modify the template.
The template lives at:
And to override it you can change
{{d-button action="showCreateAccount" label="signup_cta.sign_up" icon="check" class="btn-primary"}}
To something like:
<a href="https://foo.bar" target="_blank">Sign up</a>
In the following:
<script type="text/x-handlebars" data-template-name="components/signup-cta">
<div class="signup-cta alert alert-info">
{{#if session.hideSignupCta}}
<p>
{{i18n "signup_cta.hidden_for_session"}}
</p>
{{else}}
<p>{{replace-emoji (i18n "signup_cta.intro")}}</p>
<p>{{replace-emoji (i18n "signup_cta.value_prop")}}</p>
<div class="buttons">
{{d-button action="showCreateAccount" label="signup_cta.sign_up" icon="check" class="btn-primary"}}
{{d-button action="hideForSession" label="signup_cta.hide_session" class="no-icon"}}
<a {{action "neverShow"}}>{{i18n "signup_cta.hide_forever"}}</a>
</div>
{{/if}}
<div class="clearfix"></div>
</div>
</script>
And then add it to the </head>
section of a theme.
Let me know if you need more help.