Yes. It'll revert back to original RM number. since it cleans and reinstalls entire OS. It seems like Windows 10 For phones TP installs like in-place upgrade over 8.1.1 that's why you don't see that many apps installing when you are done with Windows 10 for phone TP, which normally happens when you upgrade ur OS.
Also it's advisable to have denim firmware before upgrading to Windows 10 since there are reports that it works better with Denim than with Cyan, Black.