If you REWAT a form 5 DEWAT C&R machinegun.  Does it have to be marked as myself being the maker?    Do C&R guns have an exemption?   Form 1 is the correct form I assume.

Yes, Form 1 to REWAT and you must mark it as you would any other Form 1 gun. There's no exemption for C&R guns.

Really?  I always thought that with a registered DEWAT, you are not the manufacturer, as it never stopped being a "firearm", you are just changing it's taxable status.

10.1.5.1 Reactivation of DEWATS. Deactivated War Trophy (DEWAT) firearms may be returned to a serviceable condition. A DEWAT that has been returned to a serviceable condition (or reactivated) is often referred to as Reactivated War Trophy (REWAT). The act of returning a DEWAT to a serviceable condition is considered the “making” or “manufacturing” of a firearm by ATF. The procedures for reactivation by a non-FFL or FFL with other than a manufacturer’s SOT status or with no SOT status on Form 1 are found in section 6.6 of the handbook. The procedures for reactivation by an FFL with SOT status as a manufacturer are found in section 7.3.3 of the handbook.