To enable additional URL prefixes to be clickable, a new feature is included in the
November 1, 2016, update (KB3127934) for Lync 2013 (Skype for Business).
After you install the update, a new client policy entry named CustomSafeUrlPrefixes must be created and added to your client policies. The value of this client policy entry should be the list of URL prefixes which should be made clickable in your organization. Each URL prefix in the list should end with a colon, and no separator is allowed between URL prefixes listed. It's supported to add up to 20 additional URL prefixes.
For example, you can create a new policy entry to enable two additional clickable URL prefixes, and add it to the global client policy:
$a = New-CsClientPolicyEntry -Name CustomSafeUrlPrefixes -Value "myprotocol:someprotocol:"
Set-CsClientPolicy -PolicyEntry @{Add=$a}
Warning If the value of this client policy entry is configured incorrectly, it could cause the registration of all clickable URL prefixes to fail. This makes all links unclickable in the Lync 2013 (Skype for Business) client. All additions and changes to this client policy entry should be evaluated and tested carefully to make sure that it's working correctly.
Note Lync 2013 was upgraded to Skype for Business in April 2015.