If there is just one ucr policy connected at the root, it is not possible, to connect an other one via UMC. The button NEW ENTRY is not visible by default, when there is just one ucr policy attached, but if you create an other ucr policy and connect it via udm to the root, then you get the NEW ENTRY Button in the UMC and both ucr policys are attached and shown.
To add a second ucr policy you can use this command for example. You have to adjust the policy of course
udm container/dc modify --dn $(ucr get ldap/base) --policy-reference='cn=office365sync,cn=config-registry,cn=policies,dc=schein,dc=ig' --policy-reference='cn=o365debug,cn=config-registry,cn=policies,dc=schein,dc=ig'