Is it possible to add SRV-records manually in H-Sphere?
You may create the records in following way:
1) convert zone file to text format (please, see https://kb.odin.com/en/119924)
2) insert SRV records
3) convert zone file back to binary format
Be aware: H-Sphere rewrites zone files with settings from its database. So you will have to monitor manually added SRV-records using a script.