Jira Service Management login page template

Hi.

I am using JSM version 5.12.12.
I want to add custom button on customer portal login page.
I found this plugin /var/atlassian/application-data/jira/plugins/installed-plugins/jira-servicedesk-5.12.12-REL-0002.jar and inside a soy template for login page /soy/cv-login-form.soy.

Adding custom HTML code with button and restaring application does not make any change.
Do you know why this approach doesnt work?