Disclaimer: This feature is now included with Advanced Request Offering feature for portal 9.4.1 and above. It is recommended to remove the Class Extension included in this post before upgrading to the later Advanced request offering management packs to avoid SCSM Datawarehouse MPSync Issues
Re-post of the workaround posted in feature request here; thought id also build the example out further - its really just an export of a SR RO MP that also contains a CR template where ive tweaked the target template from SR to CR versioned up and reimported.
Hopefully will help as an example to build out a change request process using the service catalog and advanced request offering for dynamic questions to ensure Analysts are not skipping the key information Change Managers always pestering your about

I've attached the sample MP near the end - only gotcha is you cant use multi mapping as the extended property does not exist on the CR class (update: Tested and confirmed you can if you extend) . You also need to ensure that the users have change request role access so would recommend catalog scoping to the appropriate role or just for Analysts.