Appending the trunk name is unlikely to work for your scenario if using a forward and not using the softphone or other IP-phone connected to the system. The reason being that this is an alphanumeric entry that would fall more so into the CNAM area rather than the CID and is used for inbound delivery so that people can associate am incoming call to a specific purpose and answer same according to the need.
There are areas where CNAM can be entered for outbound, but this is dependent upon the delivering carrier accommodating the field. In Canada, there are some that will, but I am not aware that any US carriers do (not that I know them all). I cannot speak to other countries. US carriers rely upon CID and upon receiving same, do a “dip” into a database and retrieve the CNAM listed as being associated to the CID and deliver same …assuming the receiving subscriber has CNAM delivery included in their subscription plan.
There are various fields in the SIP headers which your provider may use to determine the CID (from, rpid, PPI and PAI). Unfortunately, you may have to do some trial and error as the settings in the UCM are impacted by how you set CID in the extension level, DOD and/or global levels along with the settings used in the trunk as well as what the provider expects. The settings usually have a precedence as to how/when applied. You are correct in that how it works has changed and this is due to the added flexibility that has since been incorporated with new features.
The other needs of the user-base may also come into play as it was not mentioned if all outbound calls should only show the primary business number, should show a DID for each so equipped extension (private line), or ???. if only the primary number then you can do at the trunk level or even perhaps at the provider as some have user portals that allow user interaction such that you can put an override in place so that the provider will output the CID for any/all calls.