Upgrade from 12.1 RU4 to RU4 MP1b

Good morning,

We are planning to go from RU4 to RU4 MP1b, and have couple of quick questions.  I know we can follow http://www.symantec.com/business/support/index?page=content&id=HOWTO80759 for the procedure.

1. Will there be any issue when MP1b is applied to SEPM and the clients are still running RU4 without MP1b?

2. Will client upgrade force reboots on client machine?  (I understand reboot is needed to finish the upgrade, but will reboot be forced?).

Thanks in advance for any help,