I have a CZ 550 in 416 Rigby and I want to rechamber it to 577 Tyrannosaur is this possible???????

Sure. However, the nominal bolt diameter of a cz550 is .700 and the 577 Ty has a rim diameter of .688", leaving not much of a lip to hold the case in place.

Further, right now nobody makes brass for the 577 Ty.

The 585 nyati would be a better choice, considering dimensions and brass availability, IMHO.

Frankly the answer is no for the reason that 500grs quoted. .012 bolt rim is not a rim at all and will shear off the first time you try it. Thus, you will have no cartridge control on feeding or ejection. Big Problem unless you like single shots. You need a bolt with a diameter of at least .725 to have enough metal for a .688 rim. The CZ550 won't cut it. A BBK02 action is OK if you can find one. The alternatives are all custom actions or a highly modified 1917 Enfield. Read- you will spend big bucks.
The other thing to consider is most of these big guns including the Nyati are shot once,dropped once and sold once guns. Most people can't handle them and they are such special purpose items that they are hard to sell.
With that said there are the really sick here on this site that actually enjoy shooting them.-Rob

A much better choice would be the 416 Rigby necked up to 470. See my post on your 475 A&M question.