Add custom email placeholders

my_template_tags.php

<?php

// Add role-specific content to the email template.
add_filter( 'um_template_tags_patterns_hook', 'my_template_tags_patterns', 10, 1 );
add_filter( 'um_template_tags_replaces_hook', 'my_template_tags_replaces', 10, 1 );
function my_template_tags_patterns( $search ) {
	$search[] = '{welcome_content_for_subscriber}';
	$search[] = '{welcome_content_for_customer}';
	$search[] = '{welcome_content_for_um_member}';
	return $search;
}
function my_template_tags_replaces( $replace ) {
	$role = um_user( 'role' );
	$replace[] = 'subscriber' === $role ? 'This message is shown in the welcome email for users whose priority user role is "Subscriber".' : '';
	$replace[] = 'customer' === $role ? 'This message is shown in the welcome email for users whose priority user role is "Customer".' : '';
	$replace[] = 'um_member' === $role ? 'This message is shown in the welcome email for users whose priority user role is "Member".' : '';
	return $replace;
}

This code is an example for the Ultimate Member plugin.

Related documentation: Emails Tab, Placeholders for email templates

See details here